Image forming apparatus

Abstract

To provide an image forming apparatus that can easily and appropriately set a change width in a first step of test voltage during chart formation according to a recording material to appropriately adjust transfer voltage.SOLUTION: An image forming apparatus has: an image carrier; a transfer member; an application unit; a detection unit that detects a voltage value or a current value when the application unit applies voltage to the transfer member; and a control unit that causes the application unit to apply a plurality of test voltages to the transfer member to form, on a recording material, a chart to which a plurality of test images are transferred, and can execute an adjustment mode for adjusting a transfer voltage applied to the transfer member by the application unit during transfer of toner images, the adjustment mode for changing the test voltages to gradually increase or decrease the absolute value of the test voltages. The control unit can change a change width in a first step of the test voltages applied during the formation of the chart based on a result of detection performed by the detection unit when voltage is applied to the transfer member while the recording material on which the chart is formed is at a transfer unit.SELECTED DRAWING: Figure 9

Description

Technical Field

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

Background Art

[0002] Conventionally, as an image forming apparatus using an electrophotographic method or the like, there is one in which a toner image formed on a photoreceptor is first transferred onto an intermediate transfer member and then secondarily transferred from the intermediate transfer member onto a recording material. There is also one that directly transfers the toner image formed on the photoreceptor onto the recording material. The transfer of the toner image from an image carrier such as a photoreceptor or an intermediate transfer member to the transfer medium is often performed electrostatically by applying a transfer voltage to a transfer member that forms a transfer portion in contact with the image carrier.

[0003] It is important to set the transfer voltage to an appropriate value when electrostatically transferring the toner image on the image carrier onto the recording material in order to obtain a high-quality image product. When the transfer voltage is insufficient for the amount of charge carried by the toner on the image carrier, the toner image may not be sufficiently transferred from the image carrier onto the recording material, and a desired image density may not be obtained. This image defect is sometimes called "bosho". Also, when the transfer voltage is too high, discharge occurs in the transfer portion, and the charging polarity of the toner on the image carrier may be reversed due to the discharge, etc., and the toner image on the image carrier may not be partially transferred onto the recording material, resulting in a partial white dropout of the image. This image defect is sometimes called "tsukinukeru".

[0004] The amount of charge required to transfer the toner on the image carrier onto the recording material varies depending on factors such as the size of the recording material and the area ratio of the toner image. Therefore, the transfer voltage supplied to the transfer portion is often applied as a constant voltage that outputs a constant voltage corresponding to a predetermined current density. This is because, regardless of the current flowing through the outside of the recording material or the portion of the recording material where there is no toner image, a transfer current corresponding to the predetermined voltage can be ensured in the portion where the important toner image is transferred.

[0005] The transfer voltage can be determined based on the transfer partial voltage corresponding to the electrical resistance of the transfer unit detected in the previous rotation process before image formation or the like, and the recording material partial voltage corresponding to the type of recording material set in advance. Thereby, an appropriate transfer voltage can be set according to environmental variations, the usage history of the transfer member, the type of recording material, and the like. However, depending on the recording material, there may be an excess or deficiency in the transfer voltage with the preset default recording material partial voltage. Therefore, it has been proposed to provide an image forming apparatus with an adjustment mode that enables adjustment of the set value of the transfer voltage according to the recording material actually used for image formation.

[0006] In Patent Document 1, an image forming apparatus having an adjustment mode for adjusting the set value of the transfer voltage has been proposed. In this adjustment mode, a chart (adjustment chart) in which a plurality of patches (test images) are transferred by switching the transfer voltage (test voltage) for each patch is formed on the recording material and output. This chart is read by a reading device provided in the image forming apparatus, and the density of each patch is detected. Then, appropriate transfer voltage conditions are selected according to the detection result.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] In the conventional adjustment mode, during the formation of one chart, the transfer voltage (test voltage) is changed stepwise with a certain change width. Conventionally, the change width (here, also referred to as the "step width") of the transfer voltage (test voltage) at one stage during the formation of this chart has generally been a fixed value.

[0009] However, various recording materials are used in the market, including high-resistance recording materials with high electrical resistance and low-resistance recording materials with low electrical resistance. Also, when the usage environment of the image forming apparatus is low temperature and low humidity, the recording material dries out and becomes high-resistance, and when it is high temperature and high humidity, the recording material absorbs moisture and becomes low-resistance. Therefore, in the case of high-resistance recording materials, if the step width of the transfer voltage during chart formation is small, there is a possibility that the appropriate transfer voltage cannot be reached within one chart. On the other hand, in the case of low-resistance recording materials, if the step width of the transfer voltage during chart formation is large, the following may occur. That is, because the step is too coarse, there is a possibility of missing the appropriate transfer voltage that can balance the suppression of image defects ("boss") due to insufficient transfer voltage and the suppression of image defects ("breakthrough") due to excessive transfer voltage.

[0010] That is, when the step width of the transfer voltage during chart formation is constant as in the conventional case, the adjustable range of the transfer voltage may become narrower than the required range, or it may become difficult to adjust to the appropriate transfer voltage because the step of the transfer voltage is too coarse.

[0011] Note that there are configurations in which the user can manually change the above step width, and configurations in which the above step width is changed according to the type of recording material manually set by the user. However, manual setting by the user is required, and the above step width is uniformly changed during the formation of one chart. However, when executing the adjustment mode, it is often difficult for the user to accurately predict the states of various recording materials and manually set the step width of the transfer voltage during chart formation appropriately.

[0012] Therefore, an object of the present invention is to provide an image forming apparatus capable of easily and appropriately setting the change width in one step of the test voltage during chart formation according to the recording material and appropriately adjusting the transfer voltage.

Means for Solving the Problems

[0013] The above object is achieved by an image forming apparatus according to the present invention. Briefly, the present invention According to one aspect, an image forming unit that forms a toner image, an image carrier that carries the toner image formed by the image forming unit, a transfer member that forms a transfer unit that transfers the toner image from the image carrier to a recording material, an applying unit that applies a voltage to the transfer member, a detecting unit that detects a voltage value or a current value when the applying unit applies a voltage to the transfer member, and a plurality of test toner images are transferred from the image carrier to the recording material in order to adjust the transfer voltage applied to the transfer member during image formation. A control unit configured to execute a process of a mode in which a chart formed by the above is output, wherein the plurality of test toner images include a first test toner image and a second test toner image, and the first test toner image is transferred to the recording material by a first test voltage, and the second test toner image is transferred to the recording material by a second test voltage, and the control unit, before forming the first test toner image and the second test toner image, when the recording material on which the chart is formed is in the transfer unit 、 the applying unit to the transfer member 、 predetermined of the voltage value voltage or the voltage for passing a current of a predetermined current value through the transfer member is applied, and the detected by the detecting unit when the predetermined of the voltage value voltage is applied of the current value detection result , or the detection result of the voltage value detected by the detection unit when the voltage for passing a current of the predetermined current value through the transfer member is applied Based on the above, the first test voltage and the second test voltage are corrected so as to change the difference between the first test voltage and the second test voltage. An image forming apparatus characterized by is provided . According to another aspect of the present invention, there is provided an image forming apparatus including: an image forming unit that forms a toner image; an image carrier that carries the toner image formed by the image forming unit; a transfer member that forms a transfer unit for transferring the toner image from the image carrier to a recording material; an applying unit that applies a voltage to the transfer member; a detecting unit that detects a voltage value or a current value when the applying unit applies a voltage to the transfer member; and a control unit configured to execute a process in a mode of outputting a chart formed by transferring a plurality of test toner images from the image carrier to the recording material in order to adjust a transfer voltage applied to the transfer member during image formation, wherein the plurality of test toner images are formed by applying a plurality of different test voltages to the transfer member. The plurality of test toner images include a first test toner image and a second test toner image. The first test toner image is transferred to the recording material by a first test voltage, and the second test toner image is transferred to the recording material by a second test voltage. Before forming the first test toner image and the second test toner image, when the recording material on which the chart is to be formed is in the transfer unit, 、 the applying unit applies , of a predetermined first voltage value a first of voltage and a predetermined second voltage value a second of voltage , or the first voltage for passing a current of a predetermined first current value through the transfer member and the second voltage for passing a current of a predetermined second current value through the transfer member to the transfer member, of the first voltage value and based on a first detection result detected by the detecting unit when the first of voltage is applied and a second detection result detected by the detecting unit when the second the current value voltage is applied, the first test voltage and the second test voltage are corrected so as to change a difference between the first test voltage and the second test voltage. of the second voltage value The second of voltage is applied, and a second detection result detected by the detecting unit when the second the current value voltage is applied. , or the first detection result of the voltage value detected by the detection unit when the first voltage for passing a current of the first current value through the transfer member is applied and the second detection result of the voltage value detected by the detection unit when the second voltage for passing a current of the second current value through the transfer member is applied An image forming apparatus is provided which corrects the first test voltage and the second test voltage so as to change a difference between the first test voltage and the second test voltage based on the first detection result and the second detection result.

Advantages of the Invention

[0014] According to the present invention, it is possible to easily and appropriately set a change width in one step of a test voltage at the time of forming a chart according to a recording material, and appropriately adjust a transfer voltage.

Brief Description of the Drawings

[0015]

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Embodiments for Carrying Out the Invention

[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 and Operation of the Image Forming Apparatus FIG. 1 is a schematic cross-sectional view of the image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 according to the present embodiment is a tandem type multifunction machine (having functions of a copier, a printer, and a facsimile machine) that can form a full-color image using an electrophotographic method and employs an intermediate transfer method.

[0018] As shown in FIG. 1, the image forming apparatus 1 includes an apparatus main body 10, a reading apparatus 80, a feeding unit 90, an image forming unit 40, a discharging unit 48, a control unit 30, an operation unit 70, and the like. Further, inside the apparatus main body 10, a temperature sensor 71 (FIG. 2) capable of detecting the temperature inside the machine, a humidity sensor 72 (FIG. 2) capable of detecting the humidity inside the machine, and the like are provided. The image forming apparatus 1 can form a four-color full-color image on a recording material (sheet, transfer material, recording medium, medium) according to image information (image signal) from the reading apparatus 80 or an external device 200 (FIG. 2). Examples of the external device 200 include host devices such as personal computers, or digital cameras, smartphones, and the like. The recording material S is one on which a toner image is formed. Specific examples include plain paper, a synthetic resin sheet that is a substitute for plain paper, thick paper, a sheet for an overhead projector, and the like.

[0019] The image forming unit 40 can form an image on the recording material S fed from the feeding unit (feeding device) 90 based on the image information. The image forming unit 40 includes image forming units 50y, 50m, 50c, 50k, toner bottles 41y, 41m, 41c, 41k, exposure devices 42y, 42m, 42c, 42k, an intermediate transfer unit 44, a secondary transfer device 45, and a fixing unit 46. The image forming units 50y, 50m, 50c, 50k form yellow (Y), magenta (M), cyan (C), and black (K) images, respectively. For elements having the same or corresponding functions or configurations provided for each color, the y, m, c, k at the end of the reference numeral indicating an element for any one of the colors may be omitted and they may be collectively described. The image forming apparatus 1 can also form a monochromatic image such as a black monochromatic image or a multi-color image using a desired single or several image forming units 50.

[0020] The image forming unit 50 has the following means. First, it has a photosensitive drum 51 which is a drum-shaped (cylindrical) photosensitive member (electrophotographic photosensitive member) as the first image carrier. It also has a charging roller 52 which is a roller-type charging member as the charging means. It also has a developing device 20 as the developing means. It also has a pre-exposure device 54 as the charge removing means. It also has a drum cleaning device 55 as the photosensitive member cleaning means. The image forming unit 50 forms a toner image on the intermediate transfer belt 44b which will be described later. The image forming unit 50 is unitized integrally as a process cartridge and is detachable from the apparatus main body 10.

[0021] The photosensitive drum 51 can carry and move (rotate) an electrostatic image (electrostatic latent image) and a toner image. In this embodiment, the photosensitive drum 51 is a negatively chargeable organic photosensitive member (OPC) with an outer diameter of 30 mm. The photosensitive drum 51 has an aluminum cylinder as the base and a surface layer formed on its surface. In this embodiment, as the surface layer, it has three layers, an undercoat layer, a photogeneration layer, and a charge transport layer, which are applied and laminated on the base in the following order. When the image forming operation is started, the photosensitive drum 51 is rotationally driven in the direction of the arrow in the figure (counterclockwise direction) at a predetermined process speed (peripheral speed) by a motor (not shown) as the driving means.

[0022] The surface of the rotating photosensitive drum 51 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by the charging roller 52. In this embodiment, the charging roller 52 is a rubber roller that contacts the surface of the photosensitive drum 51 and rotates passively as the photosensitive drum 51 rotates. A charging power source 73 (FIG. 2) is connected to the charging roller 52. The charging power source 73 applies a predetermined charging voltage (charging bias) to the charging roller 52 during the charging process.

[0023] The surface of the charged photosensitive drum 51 is scanned and exposed based on image information by the exposure device 42, and an electrostatic image is formed on the photosensitive drum 51. In this embodiment, the exposure device 42 is a laser scanner. The exposure device 42 emits laser light according to the color-separated image information output from the control unit 30 and scans and exposes the surface (outer peripheral surface) of the photosensitive drum 51.

[0024] The electrostatic image formed on the photosensitive drum 51 is developed (visualized) by supplying toner by the developing device 20, and a toner image is formed on the photosensitive drum 51. In this embodiment, the developing device 20 contains a two-component developer including non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as a developer. Toner is supplied to the developing device 20 from the toner bottle 41. The developing device 20 has a developing sleeve 24. The developing sleeve 24 is made of a non-magnetic material such as aluminum or non-magnetic stainless steel (aluminum in this embodiment). Inside the developing sleeve 24, a magnetic roller, which is a roller-shaped magnet, is fixedly arranged so as not to rotate with respect to the main body (developing container) of the developing device 20. The developing sleeve 24 carries the developer and conveys it to the developing area facing the photosensitive drum 51. A developing power source 74 (FIG. 2) is connected to the developing sleeve 24. The developing power source 74 applies a predetermined developing voltage (developing bias) to the developing sleeve 24 during the developing process. In this embodiment, toner charged with the same polarity as the charging polarity of the photosensitive drum 51 (negative polarity in this embodiment) adheres to the exposed portion (image portion) on the photosensitive drum 51 where the absolute value of the potential has decreased after being uniformly charged and then exposed (reverse development). In this embodiment, the normal charging polarity of the toner, which is the charging polarity of the toner during development, is negative.

[0025] The intermediate transfer unit 44 is arranged so as to face the four photosensitive drums 51y, 51m, 51c, and 51k. The intermediate transfer unit 44 has an intermediate transfer belt 44b which is an endless belt serving as a second image carrier. The intermediate transfer belt 44b is wound around a driving roller 44a, a driven roller 44d, and a secondary transfer inner roller 45a as a plurality of tension rollers (support rollers), and is tensioned with a predetermined tension. The intermediate transfer belt 44b can carry (rotate) while carrying the toner image. The driving roller 44a is rotationally driven by a motor (not shown) as driving means. The driven roller 44d is a tension roller that controls the tension of the intermediate transfer belt 44b to be constant. The driven roller 44d is applied with a force that pushes the intermediate transfer belt 44b from the inner peripheral surface side to the outer peripheral surface side by the biasing force of a tension spring (not shown) as biasing means. Due to this force, a tension of about 2 to 5 kg is applied in the conveyance direction of the intermediate transfer belt 44b. The secondary transfer inner roller 45a constitutes a secondary transfer device 45 as will be described later. The intermediate transfer belt 44b is rotationally driven (circumferentially moved) in the direction of the arrow in the figure (clockwise direction) at a predetermined circumferential speed corresponding to the circumferential speed of the photosensitive drum 51 when the driving roller 44a is rotationally driven and a driving force is input. Further, on the inner peripheral surface side of the intermediate transfer belt 44b, primary transfer rollers 47y, 47m, 47c, and 47k which are roller-type primary transfer members as primary transfer means are arranged corresponding to the respective photosensitive drums 51y, 51m, 51c, and 51k. The primary transfer roller 47 sandwiches the intermediate transfer belt 44b between the primary transfer roller 47 and the photosensitive drum 51. Thereby, the primary transfer roller 47 abuts on the photosensitive drum 51 via the intermediate transfer belt 44b, and a primary transfer portion (primary transfer nip) N1 where the photosensitive drum 51 and the intermediate transfer belt 44b abut is formed.

[0026] The toner image formed on the photosensitive drum 51 is primarily transferred onto the rotating intermediate transfer belt 44b in the primary transfer section N1. A primary transfer power supply 75 (Fig. 2) is connected to the primary transfer roller 47. During the primary transfer process, the primary transfer power supply 75 applies a primary transfer voltage (primary transfer bias), which is a DC voltage with a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment), to the primary transfer roller 47. For example, when forming a full-color image, the yellow, magenta, cyan, and black toner images formed on the respective photosensitive drums 51y, 51m, 51c, and 51k are sequentially and primarily transferred onto the intermediate transfer belt 44b so as to be superimposed thereon. The primary transfer power supply 75 is connected to a voltage detection sensor 75a for detecting the output voltage and a current detection sensor 75b for detecting the output current (Fig. 2). In this embodiment, the primary transfer power supplies 75y, 75m, 75c, and 75k are provided for the respective primary transfer rollers 47y, 47m, 47c, and 47k, and the primary transfer voltages applied to the primary transfer rollers 47y, 47m, 47c, and 47k can be individually controlled.

[0027] Here, in this embodiment, the primary transfer roller 47 has an elastic layer of ion-conductive foamed rubber (NBR rubber) and a core metal. The outer diameter of the primary transfer roller 47 is, for example, 15 to 20 mm. Also, as the primary transfer roller 47, the electrical resistance value is 1×10 5 ~1×10 8A roller of Ω(N / N(23°C, 50%RH) measurement, 2 kV applied) can be preferably used. Also, in this embodiment, the intermediate transfer belt 44b is an endless belt having a three-layer structure including a base layer, an elastic layer, and a surface layer in this order from the inner peripheral surface side to the outer peripheral surface side. As the material constituting the base layer, a material containing an appropriate amount of carbon black as an antistatic agent in a resin such as polyimide or polycarbonate or various rubbers can be preferably used. The thickness of the base layer is, for example, 0.05 to 0.15 mm. As the elastic material constituting the elastic layer, a material containing an appropriate amount of an ion conductive agent in various rubbers such as urethane rubber or silicone rubber can be preferably used. The thickness of the elastic layer is, for example, 0.1 to 0.500 mm. As the material constituting the surface layer, a resin such as a fluororesin can be preferably used. The surface layer reduces the adhesion of toner to the surface of the intermediate transfer belt 44b and facilitates the transfer of toner to the recording material S in the secondary transfer portion N2 described later. The thickness of the surface layer is, for example, 0.0002 to 0.020 mm. In this embodiment, the surface layer is made of, for example, one type of resin material such as polyurethane, polyester, or epoxy resin, or two or more types of materials among elastic materials such as elastic rubber, elastomer, or butyl rubber as a base material. Then, for this base material, powders or particles such as fluororesin are dispersed as a material that reduces surface energy and enhances lubricity, one type or two or more types, or with different particle sizes, to form the surface layer. In this embodiment, the intermediate transfer belt 44b has a volume resistivity of 5×10 8 ~1×10 14 Ω·cm (23°C, 50%RH) and a hardness of 60 to 85° (23°C, 50%RH) in MD1 hardness. Also, in this embodiment, the static friction coefficient of the intermediate transfer belt 44b is 0.15 to 0.6 (23°C, 50%RH, type 94i manufactured by HEIDON). Note that the intermediate transfer belt 44b has a three-layer structure in this embodiment, but a single-layer structure of a material corresponding to the above base layer may be used, for example.

[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 as a secondary transfer means and constitutes a secondary transfer device 45 together with the secondary transfer inner roller 45a, is disposed. The secondary transfer outer roller 45b sandwiches the intermediate transfer belt 44b between it and the secondary transfer inner roller 45a. As a result, the secondary transfer outer roller 45b abuts on the secondary transfer inner roller 45a via the intermediate transfer belt 44b, and a secondary transfer portion (secondary transfer nip) N2 where the intermediate transfer belt 44b and the secondary transfer outer roller 45b abut is formed. The toner image formed on the intermediate transfer belt 44b is secondarily transferred onto the recording material S that is being conveyed while being sandwiched between the intermediate transfer belt 44b and the secondary transfer outer roller 45b in the secondary transfer portion N2. In this embodiment, a secondary transfer voltage (secondary transfer bias) is applied to the secondary transfer outer roller 45b during the secondary transfer process.

[0029] Thus, in this embodiment, the secondary transfer device 45 includes a secondary transfer inner roller 45a as a facing member and a secondary transfer outer roller 45b as a secondary transfer member. The secondary transfer inner roller 45a is disposed to face the secondary transfer outer roller 45b via the intermediate transfer belt 44b. A secondary transfer power source 76 (FIG. 2), which is a voltage application means (application section), is connected to the secondary transfer outer roller 45b. During the secondary transfer process, the secondary transfer power source 76 applies a secondary transfer voltage (secondary transfer bias), which is a DC voltage having a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment), to the secondary transfer outer roller 45b. A voltage detection sensor 76a for detecting the output voltage and a current detection sensor 76b for detecting the output current are connected to the secondary transfer power source 76 (FIG. 2). Also, in this embodiment, the core metal of the secondary transfer inner roller 45a is connected to the ground potential. That is, in this embodiment, the secondary transfer inner roller 45a is electrically grounded (connected to the ground). When the recording material S is supplied to the secondary transfer section N2, a constant voltage-controlled secondary transfer voltage having a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer outer roller 45b. In this embodiment, for example, a secondary transfer voltage of 1 to 7 kV is applied, and a current of 40 to 120 μA flows, so that the toner image on the intermediate transfer belt 44b is secondarily transferred onto the recording material S. Note that in this embodiment, the secondary transfer voltage is applied to the secondary transfer section N2 by the secondary transfer power source 76 applying a DC voltage to the secondary transfer outer roller 45b, but the present invention is not limited to such an aspect. For example, the secondary transfer voltage may be applied to the secondary transfer section N2 by the secondary transfer power source 76 applying a DC voltage to the secondary transfer inner roller 45a. In this case, a DC voltage having the same polarity as the normal charging polarity of the toner is applied to the secondary transfer inner roller 45a as the secondary transfer member, and the secondary transfer outer roller 45b as the facing member is electrically grounded. In this embodiment, the secondary transfer outer roller 45b has an elastic layer of ion-conductive foamed rubber (NBR rubber) and a core metal. The outer diameter of the secondary transfer outer roller 45b is, for example, 20 to 25 mm. Also, as the secondary transfer outer roller 45b, a roller having an electrical resistance value of 1×10 5 ~1×10 8 Ω (measured at N / N (23°C, 50% RH), with 2 kV applied) can be preferably used.

[0030] The recording material S is fed from the feeding unit 90 in parallel with the above-described toner image forming operation. That is, the recording material S is loaded and stored in a recording material cassette 91 as a recording material storage unit. The recording material S stored in the recording material cassette 91 is sent out to a conveyance path 93 by a feeding roller 92 or the like as a feeding member. The recording material S sent out to the conveyance path 93 is conveyed to a registration roller pair 43 as a conveyance member by a conveyance roller pair 94 or the like as a conveyance member. The recording material S is corrected for skew by the registration roller pair 43 and supplied to the secondary transfer unit N2 in synchronization with the toner image on the intermediate transfer belt 44b. The feeding unit 90 is constituted by the recording material cassette 91, the feeding roller 92, the conveyance path 93, the conveyance roller pair 94, and the like.

[0031] The recording material S onto which the toner image has been transferred is conveyed to a fixing unit (fixing device) 46 as a fixing means. The fixing unit 46 includes a fixing roller 46a and a pressure roller 46b. The fixing roller 46a incorporates a heater as a heating means. The recording material S carrying the unfixed toner image is nipped and conveyed between the fixing roller 46a and the pressure roller 46b, thereby being heated and pressurized. As a result, the toner image is fixed (melted and adhered) onto the recording material S. Note that the temperature of the fixing roller 46a (fixing temperature) is detected by a fixing temperature sensor 77 (FIG. 2).

[0032] The recording material S on which the toner image is fixed is conveyed by a discharge roller pair 48b, etc. as a conveying member through a discharge path 48a, discharged (output) from a discharge port 48c, and loaded on a discharge tray 48d provided outside the apparatus main body 10. The discharge path 48a, the discharge roller pair 48b, the discharge port 48c, the discharge tray 48d, etc. constitute a discharge unit (discharge device) 48. Further, in this embodiment, the image forming apparatus 1 is capable of forming images on both sides of the recording material S (double-sided image formation (double-sided printing, automatic double-sided printing)). Between the fixing unit 46 and the discharge port 48c, there is provided a reverse conveyance path 12 for reversing the recording material S after the toner image is fixed on the first side and supplying it again to the secondary transfer unit N2. During double-sided image formation, the recording material S after the toner image is fixed on the first side is guided to the reverse conveyance path 12. This recording material S has its conveyance direction reversed by a switchback roller pair 13 provided in the reverse conveyance path 12 and is guided to a double-sided conveyance path 14. Then, this recording material S is sent out to a conveyance path 93 by a re-conveyance roller pair 15 provided in the double-sided conveyance path 14, conveyed to the registration roller pair 43, and supplied to the secondary transfer unit N2 by the registration roller pair 43. Thereafter, this recording material S has the toner image secondarily transferred to the second side in the same manner as when forming the image on the first side, and after the toner image is fixed, it is discharged to the discharge tray 48d. The reverse conveyance path 12, the switchback roller pair 13, the double-sided conveyance path 14, the re-conveyance roller pair 15, etc. constitute a double-sided conveyance unit (double-sided conveyance device) 11. By the operation of the double-sided conveyance unit 11, images can be formed on both sides of a single recording material S.

[0033] After the first transfer, the surface of the photosensitive drum 51 is discharged by the pre-exposure device 54. Also, deposits such as toner (residual toner after the first transfer) that remain on the photosensitive drum 51 without being transferred to the intermediate transfer belt 44b during the first transfer process are removed from the photosensitive drum 51 by the drum cleaning device 55 and recovered. The drum cleaning device 55 scrapes off deposits from the surface of the rotating photosensitive drum 51 with a cleaning blade as a cleaning member that contacts the surface of the photosensitive drum 51 and stores them in a cleaning container. The cleaning blade is in contact with the surface of the photosensitive drum 51 with a predetermined pressing force such that the tip of the free end side thereof faces the counter direction on the upstream side in the rotation direction of the photosensitive drum 51. Further, the intermediate transfer unit 44 has a belt cleaning device 60 as intermediate transfer body cleaning means. Deposits such as toner (residual toner after the second transfer) that remain on the intermediate transfer belt 44b without being transferred to the recording material S during the second transfer process are removed from the intermediate transfer belt 44b by the belt cleaning device 60 and recovered.

[0034] On the upper part of the apparatus main body 10, a reading device 80 as a reading means (reading unit) is arranged. The reading device 80 includes an automatic document feeder (ADF) 81 as a document conveyance means (document conveyance unit), a platen glass 82, a light source 83, an optical system 84 including a mirror group 84a and an imaging lens 84b, and a reading element 85 such as a CCD. In this embodiment, the reading device 80 can sequentially read an image of a document (recording material S with an image formed thereon) arranged on the platen glass 82 by the movable light source 82 while performing scanning exposure, through the optical system 84, by the reading element 85. In this case, the reading device 80 sequentially illuminates the document arranged on the platen glass 82 with the moving light source 83, and sequentially forms an image of the reflected light image from the document on the reading element 85 through the optical system 84. Thereby, the reading element 85 can read the image of the document at a predetermined dot density. Also, in this embodiment, the reading device 80 can sequentially expose an image of a document conveyed by the automatic document feeder 81 with the light source 82 as the document is conveyed, and sequentially read it by the reading element 85 through the optical system 84. In this case, the reading device 80 sequentially illuminates the document passing through a predetermined reading position on the platen glass 82 with the light source 83, and sequentially forms an image of the reflected light image from the document on the reading element 85 through the optical system 84. Thereby, the reading element 85 can read the image of the document at a predetermined dot density. Thus, the reading device 80 optically reads an image on the recording material S arranged on the platen glass 82 or conveyed by the automatic document feeder 81 and converts it into an electrical signal.

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

[0036] FIG. 2 is a block diagram showing a schematic configuration of the control system of the image forming apparatus 1 according to the present embodiment. As shown in FIG. 2, the control unit 30 is configured by a computer. The control unit 30 includes, for example, a CPU 31 as arithmetic control means, a ROM 32 as storage means for storing a program for controlling each unit, a RAM 33 as storage means for temporarily storing data, and an input / output circuit (I / F) 34 for inputting / outputting signals to / from the outside. The CPU (arithmetic unit) 31 is a microprocessor that controls the overall control of the image forming apparatus 1 and is the main body of the system controller. The CPU 31 is connected to the feeding unit 90, the image forming unit 40, the discharging unit 48, and the operation unit 70 via the input / output circuit 34, exchanges signals with these units, and controls the operations of these units. The ROM 32 stores an image forming control sequence and the like for forming an image on the recording material S. A charging power source 73, a developing power source 74, a primary transfer power source 75, and a secondary transfer power source 76 are connected to the control unit 30, and these are controlled by signals from the control unit 30, respectively. Further, a temperature sensor 71, a humidity sensor 72, a voltage detection sensor 75a and a current detection sensor 75b of the primary transfer power source 75, a voltage detection sensor 76a and a current detection sensor 76b of the secondary transfer power source 76, and a fixing temperature sensor 77 are connected to the control unit 30. Signals detected by each sensor are input to the control unit 30.

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

[0038] In this embodiment, the control unit 30 includes an image formation pre - preparation process unit 31a, an ATVC control process unit 31b, an image formation process unit 31c, and an adjustment process unit 31d. Further, the control unit 30 includes a primary transfer voltage storage / operation unit 31e and a secondary transfer voltage storage / operation unit 31f. Note that each of these process units and storage / operation units may be provided as a part of the CPU 31 and the RAM 33. For example, the control unit 30 (more specifically, the image formation process unit 31c) can execute a job. Also, the control unit 30 (more specifically, the ATVC control process unit 31b) can execute ATVC control (setting mode) for the primary transfer unit and the secondary transfer unit. The ATVC control will be described in detail later. Further, the control unit 30 (more specifically, the adjustment process unit 31d) can execute an adjustment mode for adjusting the set value of the secondary transfer voltage. The adjustment mode will be described in detail later.

[0039] Note that in this embodiment, the control unit 30 (image formation process unit 31c) can switch between and execute a multi - color mode in which a primary transfer voltage is applied to a plurality of primary transfer units N1 to form multi - color images, and a single - color mode in which a primary transfer voltage is applied to only one of the plurality of primary transfer units N1 to form a single - color image.

[0040] Here, the image forming apparatus 1 executes a job (image output operation, printing job), which is a series of operations for forming and outputting an image on a single or a plurality of recording materials S started by one start instruction. The job generally includes an image forming process, a pre-rotation process, an intersheet process when forming an image on a plurality of recording materials S, and a post-rotation process. The image forming process is a period during which an electrostatic image of the image actually formed and output on the recording material S, a toner image is formed, a primary transfer of the toner image, and a secondary transfer are performed. The time during image formation (image formation period) refers to this period. More specifically, the timings during image formation are different at the positions where these processes of forming an electrostatic image, forming a toner image, primary transferring the toner image, and secondary transferring the toner image are performed. The pre-rotation process is a period during which preparatory operations before the image forming process are performed from when a start instruction is input until actually starting to form an image. The intersheet process is a period corresponding to between the recording materials S when continuously forming an image on a plurality of recording materials S (continuous image formation). The post-rotation process is a period during which sorting operations (preparatory operations) after the image forming process are performed. The time during non-image formation (non-image formation period) is a period other than the time during image formation, and includes the above-mentioned pre-rotation process, intersheet process, post-rotation process, and further a pre-multi-rotation process, which is a preparatory operation when the image forming apparatus 1 is powered on or resumes from a sleep state.

[0041] 2. Control of Secondary Transfer Voltage Next, the control of the secondary transfer voltage will be described. FIG. 3 is a flowchart showing an outline of the procedure for controlling the secondary transfer voltage in this embodiment. Generally, for the control of the secondary transfer voltage, there are constant voltage control and constant current control, but in this embodiment, constant voltage control is used.

[0042] First, when the control unit 30 (image formation pre - 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). This job information includes image information specified by the operator and information on the recording material S. The information on the recording material S may include information related to the size (width, length) of the recording material S on which an image is to be formed, information related to the thickness of the recording material S (such as thickness, basis weight, etc.), and information related to the surface property of the recording material S, such as whether the recording material S is coated paper or not. In particular, in this embodiment, the information on the recording material S includes information on the size of the recording material S and information on the category of the recording material S (so - called paper type category), such as "thin paper, plain paper, thick paper...", which is related to the thickness of the recording material S. Note that the information on the recording material S (recording material information) includes attributes (so - called paper type category) based on general characteristics such as plain paper, high - quality paper, glossy paper, gloss paper, coated paper, embossed paper, thick paper, thin paper, etc., numerical values or numerical ranges such as basis weight, thickness, size, rigidity, or a brand (including manufacturer, product name, product number, etc.). It encompasses any information that can distinguish the recording material S. Each recording material S distinguished by the information on the recording material S can be regarded as constituting the type of the recording material S. Also, the information on the recording material S may be included in the print mode information that designates the operation settings of the image forming apparatus 1, such as "plain paper mode", "thick paper mode", or may be replaced by the print mode information. The control unit 30 (image formation pre - preparation process unit 31a) writes this job information to the RAM 33 (S102).

[0043] Next, the control unit 30 (image formation preparation process unit 31a) acquires environmental information detected by the temperature sensor 71 and the humidity sensor 72 (S103). Further, the ROM 32 stores information indicating the correlation between the environmental information and the target current Itarget for transferring the toner image on the intermediate transfer belt 44b onto the recording material S. The control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) obtains the target current Itarget corresponding to the environment from the information indicating the relationship between the environmental information and the target current Itarget based on the environmental information read in S103. Then, the control unit 30 writes this target current Itarget to the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f) (S104). Note that 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 information indicating the relationship between the environmental information and the target current Itarget is obtained in advance through experiments or the like.

[0044] Next, the control unit 30 (ATVC control process unit 31b) acquires information regarding the electrical resistance of the secondary transfer unit N2 by ATVC (Active Transfer Voltage Control) before the toner image on the intermediate transfer belt 44b and the recording material S onto which the toner image is to be transferred reach the secondary transfer unit N2 (S105). That is, with the secondary transfer outer roller 45b and the intermediate transfer belt 44b in contact, a plurality of levels of predetermined voltages are supplied from the secondary transfer power supply 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 voltage and current (voltage-current characteristics) as shown in FIG. 4 is acquired. The control unit 30 writes the information on this relationship between voltage and current into the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f). This relationship between voltage and current changes according to the electrical resistance of the secondary transfer unit N2. In the configuration of the present embodiment, the relationship between the voltage and the current is not such that the current changes linearly (proportionally) with respect to the voltage, but rather the current changes such that it is represented by a polynomial of the second degree or higher (a quadratic equation in the present embodiment) of the voltage. Therefore, in the present embodiment, in order to be able to represent the relationship between the voltage and the current by a polynomial, the predetermined voltage or current supplied when acquiring information regarding the electrical resistance of the secondary transfer unit N2 is set to three or more multi-stages.

[0045] Next, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) obtains the voltage value to be applied from the secondary transfer power supply 76 to the secondary transfer outer roller 45b (S106). That is, based on the target current Itarget written in the RAM 33 in S104 and the relationship between the voltage and current obtained in S105, the control unit 30 obtains the voltage value Vb required to pass the target current Itarget through the secondary transfer unit N2 in a state where the recording material S is not present. This voltage value Vb corresponds to the secondary transfer partial voltage (transfer voltage corresponding to the electrical resistance of the secondary transfer unit N2). It should be noted that the target current Itarget may be applied from the secondary transfer power supply 76 to the secondary transfer outer roller 45b by constant current control, and the voltage value at that time may be detected by the voltage detection sensor 76a, and the detected voltage may be used as the voltage value Vb. Also, the ROM 32 stores information for obtaining the recording material partial voltage Vp (transfer voltage corresponding to the electrical resistance of the recording material S) as shown in FIG. 5. In this embodiment, this information is set as table data showing the relationship between the moisture content of the atmosphere and the recording material partial voltage Vp for each classification of the basis weight of the recording material S (corresponding to the paper type category). Note that the control unit 30 (image formation pre - preparation process unit 31a) can obtain the moisture content of the atmosphere based on the environmental information (temperature and humidity) detected by the temperature sensor 71 and the humidity sensor 72. The control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) obtains the recording material partial voltage Vp from the above table data based on the job information acquired in S101 and the environmental information acquired in S103. Also, when an adjustment value is set in the adjustment mode for adjusting the set value of the secondary transfer voltage described later, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) obtains an adjustment amount (correction amount) ΔV corresponding to the adjustment value (correction value). As will be described later, this adjustment amount ΔV is stored in the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f) when set by the adjustment mode. The control unit 30 obtains Vb + Vp+ΔV, which is the sum of the above Vb, Vp, and ΔV, as the secondary transfer voltage Vtr to be applied from the secondary transfer power supply 76 to the secondary transfer outer roller 45b when the recording material S is passing through the secondary transfer unit 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).Note that 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.

[0046] Here, the recording material shared voltage Vp may change not only depending on information related to the thickness of the recording material S (such as thickness and basis weight), but also depending on the surface property of the recording material S. Therefore, the above table data may be set such that the recording material shared voltage Vp also changes depending on information related to the surface property of the recording material S. Further, in the present embodiment, information related to the thickness of the recording material S (and further information related to the surface property of the recording material S) is included in the information of the job acquired in S101. However, a measuring means for detecting the thickness of the recording material S or the surface property of the recording material S may be provided in the image forming apparatus 1, and the recording material shared voltage Vp may be obtained based on the information obtained by this measuring means.

[0047] 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 performs secondary transfer by applying the secondary transfer voltage Vtr determined as described above (S107). Thereafter, the control unit 30 (image forming process unit 31c) repeats the process of S107 until all the images of the job are transferred to the recording material S and output is completed (S108).

[0048] Regarding the primary transfer unit N1 as well, the same ATVC control as described above is performed from when the job is started until the toner image is conveyed to the primary transfer unit N1, but detailed description thereof is omitted here.

[0049] 3. Outline of the adjustment mode Next, an adjustment mode (simple adjustment mode) for adjusting the set value of the secondary transfer voltage will be described.

[0050] Depending on the type and condition of the recording material S used for image formation, the moisture content and electrical resistance of the recording material S may be significantly different from those of the standard recording material S. In this case, the setting value of the secondary transfer voltage using the default recording material distribution voltage Vp set in advance as described above may not be able to perform appropriate transfer. In other words, the secondary transfer voltage must first be a voltage necessary for transferring the toner on the intermediate transfer belt 44b to the recording material S. In addition, the secondary transfer voltage must be suppressed to a voltage that does not cause abnormal discharge. However, depending on the type and condition of the recording material S actually used for image formation, the electrical resistance may be higher than the value assumed as the standard value. In this case, the setting value of the secondary transfer voltage using the default recording material distribution voltage Vp set in advance may not be enough to transfer the toner on the intermediate transfer belt 44b to the recording material S. Therefore, in this case, it is desirable to increase the secondary transfer voltage by increasing the recording material distribution voltage Vp, for example. Conversely, depending on the type and condition of the recording material S actually used for image formation, the recording material S may absorb moisture, and thus the electrical resistance may be lower than the value assumed as the standard value, making it easier for discharge to occur. In this case, the setting value of the secondary transfer voltage using the preset default recording material distribution voltage Vp may cause image defects due to abnormal discharge. Therefore, in this case, it is desirable to lower the secondary transfer voltage by lowering the recording material distribution voltage Vp, for example.

[0051] For this reason, it may be desirable for an operator such as a user or a service person to adjust (change) the setting value of the secondary transfer voltage during job execution to an appropriate value by, for example, adjusting (changing) the recording material assigned voltage Vp according to the recording material S actually used for image formation. In other words, it may be desirable to select an appropriate recording material assigned voltage Vp+ΔV (adjustment amount) according to the recording material S actually used for image formation.

[0052] This adjustment can also be considered to be performed in the following manner. That is, for example, the operator outputs the image to be output while switching the secondary transfer voltage for each sheet of recording material S, checks the output image, and determines an appropriate set value of the secondary transfer voltage (more specifically, the recording material sharing voltage Vp + ΔV). However, in this method, in order to repeat the output of the image and the adjustment of the set value of the secondary transfer voltage, there may be an increase in the wasted recording material S or it may take a long time for the adjustment.

[0053] Therefore, in this embodiment, the image forming apparatus 1 is provided with an adjustment mode for adjusting the set value of the secondary transfer voltage. In this adjustment mode, a chart is formed and output on the recording material S actually used for image formation by transferring a plurality of patches (test images) of representative colors while switching the secondary transfer voltage (test voltage) for each patch. Then, based on the output chart, it is possible to determine an appropriate set value of the secondary transfer voltage (more specifically, the recording material sharing voltage Vp + ΔV). In this embodiment, in the adjustment mode, based on the result of the control unit 30 reading the density information (luminance information) of the patches (typically patches of solid images) on the chart by the reading device 80, information regarding the recommended adjustment amount ΔV of the set value of the secondary transfer voltage is presented. Thereby, while reducing the necessity for the operator to visually check the image on the chart and reducing the operation burden on the operator, it becomes possible to more appropriately adjust the set value of the secondary transfer voltage.

[0054] 4. Chart Next, a chart (adjustment image, test page) output in the adjustment mode in this embodiment will be described. FIGS. 6 and 7 are schematic diagrams of a chart 100 in this embodiment. In this embodiment, in the adjustment mode, two types of charts 100 shown in FIGS. 6 and 7 are output roughly according to the size of the recording material S to be used. FIG. 6 shows a chart 100 output when the length of the recording material S in the conveyance direction is 420 to 487 mm. FIG. 7 shows a chart 100 output when the length of the recording material S in the conveyance direction is 210 to 419 mm. In this embodiment, in the adjustment mode, charts can be output on both sides of the recording material S so that the secondary transfer voltages during secondary transfer to the front side (first side) and the back side (second side) in double-sided image formation can be adjusted respectively. FIGS. 6 and 7 show charts when forming a chart (hereinafter also referred to as "single-sided chart") on one side of the recording material S, and when forming a chart (hereinafter also referred to as "double-sided chart") on both sides of the recording material S. The double-sided chart is formed by double-sided image formation using the above-described double-sided conveyance unit 11.

[0055] Here, the size of the recording material S is indicated by the recording material width (main scanning direction length) × recording material length (sub-scanning direction length). The recording material width is the length in the direction (width direction) substantially orthogonal to the conveyance direction of the recording material S when passing through the secondary transfer unit N2. Also, the recording material length is the length in the direction substantially parallel to the conveyance direction of the recording material S when passing through the secondary transfer unit N2.

[0056] FIG. 6 shows large-size charts (hereinafter also referred to as "large charts") 100L (100La, 100Lb) output when using large-size recording materials S such as A3 (297 mm × 420 mm) or ledger (about 280 mm × 432 mm). FIG. 6(a) shows the large chart 100La when outputting a single-sided chart (or the first side when outputting a double-sided chart). Also, FIG. 6(b) shows the large chart 100Lb of the second side when outputting a double-sided chart.

[0057] FIG. 7 shows a small-size chart (hereinafter also referred to as "small chart") 100S (100Sa, 100Sb) to be output when using a small-size recording material S such as A4 landscape (297 mm × 210 mm) or letter landscape (approx. 280 mm × 216 mm). FIGS. 7(a) and 7(b) show the first and second small charts 100Sa when outputting a single-sided chart (or the first side when outputting a double-sided chart). FIGS. 7(c) and 7(d) show the first and second small charts 100Sb of the second side when outputting a double-sided chart respectively.

[0058] Considering visual confirmation by the operator, the larger the size of the patch of the chart output in the adjustment mode, the more advantageous it is to confirm image defects. However, if the patch is large, the number of patches that can be formed on a single recording material S decreases. The shape of the patch can be a square or the like. The color of the patch can be determined according to the image defect to be confirmed and the ease of confirmation. For example, when the secondary transfer voltage is increased from a low value to a high value, the lower limit value of the secondary transfer voltage can be determined from the voltage value at which secondary color patches such as red, green, and blue can be appropriately transferred. Also, when the operator visually confirms, when the secondary transfer voltage is further increased, the upper limit value of the secondary transfer voltage can be determined from the voltage value at which image defects due to a high secondary transfer voltage occur in the halftone patch.

[0059] Chart 100 has a patch set in which one solid blue patch 101, one solid black patch 102, and two halftone patches 103 are arranged in the width direction. In the large chart 100L of FIG. 6, 11 sets of this patch set 101 to 103 in the width direction are arranged in the conveyance direction. In the small chart 100S of FIG. 7, 10 sets of this patch set 101 to 103 in the width direction are arranged in the conveyance direction. In this embodiment, the halftone patch 103 is a gray (black halftone) patch. Here, the solid image is an image with the maximum density level. In this embodiment, the solid blue is an overlay of magenta (M) toner = 100% and cyan (C) toner = 100%, and the toner loading amount of the solid blue is 200%. The halftone image is, for example, an image with a toner loading amount of 10 to 80% when the toner loading amount of the solid image is 100%. In this embodiment, the chart 100 is provided with patch identification information 104 for identifying the setting of the secondary transfer voltage applied to each patch set for each of the patch sets 101 to 103. This patch identification information 104 may be a value corresponding to the adjustment value of the secondary transfer voltage described later. In the large chart 100L of FIG. 6, 11 pieces (11 pieces of -5 to 0 to +5 in this embodiment) of patch identification information 104 corresponding to the setting of the 11-step secondary transfer voltage are arranged. In the small chart 100S of FIG. 7, 10 pieces (5 pieces of -4 to 0 on the first sheet and 5 pieces of +1 to +5 on the second sheet in this embodiment) of patch identification information 104 corresponding to the setting of the 10-step secondary transfer voltage are arranged. Further, the chart 100 may be provided with front-back identification information 105 indicating at least one of the front side (first side) or the back side (second side) of the recording material S on at least one of the front side (first side) or the back side (second side) of the recording material S.

[0060] The size of the patch is required to be such that it is easy for the operator to determine the presence or absence of image defects. Regarding the transferability of the blue solid patch 101 and the black solid patch 102, since it becomes difficult to make a judgment when the patch size is small, the patch size is preferably 10 mm square or larger, and more preferably 25 mm square or larger. In the case of the halftone patch 103, the image defects caused by discharge when the secondary transfer voltage is increased often become image defects such as white dots. This image defect tends to be easier to judge even for a small image compared to the transferability of the solid image. However, since it is easier to view the image when it is not too small, in this embodiment, the width of the halftone patch 103 in the conveyance direction is the same as the width of the blue solid patch 101 and the black solid patch 102 in the conveyance direction. Also, the interval between the patch sets 101 to 103 in the conveyance direction may be set so that the secondary transfer voltage can be switched. In this embodiment, the blue solid patch 101 and the black solid patch 102 are each a square of 25.7 mm × 25.7 mm (one side is substantially parallel to the width direction). Also, in this embodiment, the halftone patches 103 at both ends in the width direction each have a width of 25.7 mm in the conveyance direction and extend to the outermost ends of the chart 100 (there may be a margin as described later). Also, in this embodiment, the interval between the patch sets 101 to 103 in the conveyance direction is 9.5 mm. The secondary transfer voltage is switched at the timing when the portion on the chart 100 corresponding to this interval passes through the secondary transfer portion N2. In this embodiment, each patch set 101 to 103 of the chart 100 is sequentially transferred from the upstream side to the downstream side in the conveyance direction of the recording material S when the chart 100 is formed, using a plurality of secondary transfer voltages that are made different so that their absolute values increase sequentially. However, the present invention is not limited to such an aspect. Each patch set 101 to 103 of the chart 100 may be sequentially transferred from the upstream side to the downstream side in the conveyance direction of the recording material S when the chart 100 is formed, using a plurality of secondary transfer voltages that are made different so that their absolute values decrease sequentially. The secondary transfer voltage when the chart is formed will be described in detail later.

[0061] In addition, it is preferable not to form patches in the vicinity of the leading end and the trailing end in the conveyance direction of the recording material S (for example, in a range of about 20 to 30 mm from the edge to the inside). This is due to the following reasons. That is, among the ends of the recording material S in the conveyance direction, there may be an image defect that occurs only at the leading end or the trailing end in the conveyance direction without occurring at the end in the width direction. In this case, it may be difficult to determine whether the image defect occurred due to the application of the secondary transfer voltage.

[0062] The maximum size of the recording material S that can be used in the image forming apparatus 1 of this embodiment is 13 inches (approx. 330 mm) × 19.2 inches (approx. 487 mm), and the large chart 100L in FIG. 6 corresponds to the recording material S of this size. When the size of the recording material S is 13 inches × 19.2 inches or less and A3 (297 mm × 420 mm) or more, a chart corresponding to the image data cut out according to the size of the recording material S from the image data of the large chart 100L shown in FIG. 6 is output. At this time, in this embodiment, the image data is cut out according to the size of the recording material S with reference to the center of the leading edge. That is, the leading edge in the conveyance direction of the recording material S and the leading edge in the conveyance direction of the large chart 100L (the upper end in the figure) are aligned, and the center in the width direction of the recording material S and the center in the width direction of the large chart 100L are aligned, and the image data is cut out. Also, in this embodiment, the image data is cut out so that a margin of 2.5 mm is provided at the ends (both ends in the width direction and both ends in the conveyance direction in this embodiment). For example, when the large chart 100L is output to the A3 (297 mm × 420 mm) recording material S, the image data in the range of 292 mm × 415 mm is cut out with a margin of 2.5 mm at each end. Then, the large chart 100L corresponding to the image data is output to the A3 (297 mm × 420 mm) recording material S with reference to the center of the leading edge. When the recording material S with a width smaller than 13 inches is used, the size in the width direction of the halftone patch 103 at the end in the width direction becomes smaller. Also, when the recording material S with a width smaller than 13 inches is used, the margin at the rear end in the conveyance direction becomes smaller. As described above, 11 sets of patch sets of -5 to 0 to +5 are arranged on the large chart 100L. The 11 sets of patch sets 101 to 103 of the large chart 100L are arranged in a range with a length of 387 mm in the conveyance direction so as to fit within the length of 415 mm in the conveyance direction when the size of the recording material S is A3.

[0063] In this embodiment, when a recording material S with a size smaller than A3 (297 mm × 420 mm) is used, the small chart 100S in FIG. 7 is output. The small chart 100S in FIG. 7 corresponds to sizes smaller than A5 (longitudinal feed) to A3 (297 mm × 420 mm), that is, sizes with a length in the conveyance direction of 210 to 419 mm. As described above, on the first page of the small chart 100S, a total of 10 patch sets, 5 sets of -4 to 0 and on the second page, +1 to +5, are arranged. The size of the image data of the small chart 100S is 13 inches × 210 mm. In the width direction, the halftone patches 103 become smaller according to the size of the recording material S. In the conveyance direction, 5 sets of patch sets are arranged to fit within a length of 167 mm in the conveyance direction, and the blank space at the rear end increases according to the length in the conveyance direction of the recording material S with a length of 210 to 419 mm. In the case of a recording material S with a length in the conveyance direction of 210 to 419 mm, only 5 sets of patch sets can be formed in the conveyance direction in one sheet. Therefore, in order to increase the number of patches, the chart is divided into two sheets, with 5 sets of -4 to 0 and 5 sets of +1 to +5, to form a total of 10 sets of patch sets. Note that in the small chart 100S, the patch set of -5 in the large chart 100L is omitted.

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

[0065] Also, in this embodiment, not only standard sizes but also charts 100 can be output using a recording material S of an arbitrary size (free size) by, for example, inputting and specifying by the operator from the operation unit 70 or the external device 200.

[0066] Here, one chart 100 may be formed on one surface of a single recording material S or separately formed on one surface of each of a plurality of recording materials S (that is, one set of charts having a set of patch groups in which the test voltage is changed step by step). In the above example, the large chart 100La (first side) and the large chart 100Lb (second side) each correspond to one chart. Also, in the above example, the first and second small charts 100Sa (first side) as a whole correspond to one chart. Similarly, the first and second small charts 100Sb (second side) as a whole correspond to one chart.

[0067] 5. Operation of the adjustment mode 5-1. Conventional problems FIG. 15 is an explanatory diagram of the operation of a conventional adjustment mode. FIG. 15(a) is a graph showing the relationship between the adjustment value (horizontal axis) at the time of forming the chart 100 and the secondary transfer voltage (test voltage, applied voltage) (vertical axis). FIG. 15(b) is a graph showing the relationship between the adjustment value (horizontal axis) in the chart 100 and the luminance value of the blue beta patch (vertical axis). FIG. 15(c) is a graph showing the relationship between the secondary transfer voltage and the adjustment value (horizontal axis) at the time of forming the chart 100 and the current detected when each secondary transfer voltage is applied (vertical axis) (here, also referred to as "voltage-current characteristic"). Here, the image forming apparatus 1 applies the secondary transfer voltage under constant voltage control and detects the current at that time with a current detection sensor (current detection circuit). Also, here, the case of forming the large chart 100L as described above as the chart 100 is taken as an example.

[0068] In the conventional adjustment mode, as shown in FIG. 15(a), during the formation of one chart, the secondary transfer voltage is changed step by step at a constant step width. For example, the secondary transfer voltage is sequentially increased in steps of 150V (adjustment value -5: 150V → adjustment value -4: 300V → adjustment value -3: 450V). Conventionally, the step width of the secondary transfer voltage at the time of forming this chart 100 has generally been a fixed value.

[0069] Then, for example, when the luminance value of the blue beta patch on this chart 100 is read by the reading device 80, the relationship between the adjustment value and the luminance value as shown in FIG. 15(b) can be obtained. Here, FIG. 15(b) shows an example of the relationship between the adjustment value and the luminance value when the recording material S used for forming the chart 100 is a normal recording material S having a standard electrical resistance based on its type or the like. As the recommended adjustment value of the secondary transfer voltage in the adjustment mode, in the relationship between the adjustment value and the luminance value as shown in FIG. 15(b), an adjustment value at which the luminance value becomes sufficiently small (the density becomes high) is selected. In the illustrated example, since there is a possibility that image defects ("burn-through") may occur due to the secondary transfer voltage being too high at the adjustment value of +5, for example, the adjustment value of +1 is selected as the recommended adjustment value of the secondary transfer voltage. An example of a method for determining the recommended adjustment value of the secondary transfer voltage will be described later and further explained.

[0070] Here, when the above normal recording material S is used for forming the chart 100, the voltage-current characteristics during the formation of the chart 100 are, for example, as shown by the solid line in FIG. 15(c). In this case, it can be seen that the adjustable range of the secondary transfer voltage is sufficient for selecting the recommended adjustment value of the secondary transfer voltage. In the illustrated example, at the adjustment value of +1, the secondary transfer voltage is 1050V and the secondary transfer current is 15 μA.

[0071] On the other hand, when the recording material S used for forming the chart 100 is a high-resistance recording material S having an electrical resistance higher than the standard electrical resistance based on its type or the like, the voltage-current characteristics during the formation of the chart 100 are, for example, as shown by the broken line in FIG. 15(c). In this case, the slope (absolute value) of the voltage-current characteristics becomes smaller than that in the case of the normal recording material S. Therefore, at the step width of the secondary transfer voltage of 150V, the step width is small, and at the secondary transfer voltage of 1650V with the adjustment value of +5 (the maximum value), the secondary transfer voltage at which the luminance value of the blue beta patch becomes sufficiently small (the density becomes high) cannot be reached. That is, in this case, it can be seen that the adjustable range of the secondary transfer voltage is narrower than the range required for selecting the recommended adjustment value of the secondary transfer voltage.

[0072] Also, when the recording material S used for forming the chart 100 is a low-resistance recording material S having an electrical resistance lower than the standard electrical resistance based on its type or the like, the voltage-current characteristics during the formation of the chart 100 are as shown by the dashed-dotted line in FIG. 15(c), for example. In this case, the slope (absolute value) of the voltage-current characteristics becomes larger than that in the case of a normal recording material S. Therefore, at the step width of the secondary transfer voltage of 150V, the step width is large, and there may be a recommended adjustment value of the secondary transfer voltage between the adjustment values. For example, when the luminance value of the blue beta patch becomes sufficiently small (the density becomes high), and there is an adjustment value between adjustment values -3 and -2 (secondary transfer voltage 500V) that can sufficiently suppress image defects ("burn-through") due to the secondary transfer voltage being too high. That is, in this case, it can be seen that the step of the secondary transfer voltage is too coarse to appropriately select the recommended adjustment value of the secondary transfer voltage.

[0073] Various recording materials S are used in the market, including high-resistance recording materials S with high electrical resistance and low-resistance recording materials S with low electrical resistance. Also, when the usage environment of the image forming apparatus 1 is low temperature and low humidity, the recording material S dries out and becomes high-resistance, and when it is high temperature and high humidity, the recording material S absorbs moisture and becomes low-resistance. Therefore, as described above, in the case of a high-resistance recording material S, if the step width of the secondary transfer voltage during the formation of the chart 100 is small, there is a possibility that the appropriate secondary transfer voltage may not be reached within one chart. On the other hand, in the case of a low-resistance recording material S, if the step width of the secondary transfer voltage during the formation of the chart 100 is large, the following may occur. That is, because the step is too coarse, there is a possibility of missing the appropriate secondary transfer voltage that can achieve both suppression of image defects ("boss") due to insufficient transfer voltage and suppression of image defects ("burn-through") due to excessive transfer voltage.

[0074] 5-2. Operation of the adjustment mode of this embodiment Next, the operation of the adjustment mode in this embodiment will be described. FIGS. 8 and 9 are explanatory diagrams of the operation of the adjustment mode in this embodiment. FIG. 8(a) is a graph showing the voltage-current characteristics at the time of forming the chart 100, which is the same as FIG. 15(c). FIG. 8(b) is a graph showing the relationship between the secondary transfer voltage and the adjustment value (horizontal axis) and the luminance value of the patch of the blue beta (vertical axis) when the step width of the secondary transfer voltage (test voltage, applied voltage) is constant during the formation of the chart 100. FIGS. 9(a) and (b) are graphs showing the relationship between the secondary transfer voltage and the adjustment value (horizontal axis) and the luminance value of the patch of the blue beta (vertical axis) when the step width of the secondary transfer voltage (test voltage, applied voltage) is changed during the formation of the chart 100 according to this embodiment.

[0075] In this embodiment, the image forming apparatus 1 is configured to apply the secondary transfer voltage under constant voltage control and detect the current at that time with a current detection sensor (current detection circuit) 76b. However, the present invention is not limited to such an aspect, and the image forming apparatus 1 may be configured to apply the secondary transfer voltage under constant current control and detect the voltage at that time with a voltage detection sensor (voltage detection circuit) 76a. Further, in this embodiment, as in the example described with reference to FIG. 15, in the case of a normal recording material S, during the formation of one chart 100, the secondary transfer voltage is sequentially increased at a substantially constant step width of 150V. Further, in this embodiment, the image forming apparatus 1 is configured to read the luminance value of the patch of the blue beta of the chart 100 with a reading device 80 and determine the recommended adjustment value of the secondary transfer voltage. Here, the case of forming the large chart 100L as described above as the chart 100 is taken as an example.

[0076] As described with reference to FIG. 15, as shown in FIG. 8(a), in the case of a high-resistance recording material S, the slope of the voltage-current characteristics at the time of forming the chart 100 becomes small. Therefore, as shown in FIG. 8(b), at a step width of the secondary transfer voltage of 150V, the step width is small and the secondary transfer voltage at which the luminance value of the patch of the blue beta becomes sufficiently small (the density becomes high) is not reached.

[0077] Therefore, in this embodiment, in the case of the high-resistance recording material S, as shown in Fig. 9(a), during the formation of the chart 100, the step width of the secondary transfer voltage is changed to be increased. In the illustrated example, the step width of the secondary transfer voltage is 150 V on the lower side of the secondary transfer voltage and 300 V on the higher side of the secondary transfer voltage. That is, the step width of the secondary transfer voltage during the formation of one chart 100 is not equally spaced. As a result, even for the high-resistance recording material S, within one chart 100, the secondary transfer voltage reaches up to 2850 V at the adjusted value +5 (maximum value). And it becomes possible to select the secondary transfer voltage up to the range where the luminance value of the blue-veta patch becomes sufficiently small (the density becomes high). That is, the adjustable range of the secondary transfer voltage can be made a sufficient range.

[0078] Also, as described with reference to Fig. 15, as shown in Fig. 8(a), in the case of the low-resistance recording material S, the slope of the voltage-current characteristic during the formation of the chart 100 becomes large. Therefore, as shown in Fig. 8(b), the luminance value of the blue-veta patch rapidly becomes small (the density becomes high) with respect to the change in the secondary transfer voltage. That is, in this case, with a step width of 150 V for the secondary transfer voltage, the step width is large, and there may be a recommended adjusted value of the secondary transfer voltage between the adjusted values.

[0079] Therefore, in this embodiment, in the case of the low-resistance recording material S, as shown in Fig. 9(b), during the formation of the chart 100, the step width of the secondary transfer voltage is changed to be decreased. In the illustrated example, the step width of the secondary transfer voltage is 150 V on the lower side of the secondary transfer voltage and 75 V on the higher side of the secondary transfer voltage. That is, the step width of the secondary transfer voltage during the formation of one chart 100 is not equally spaced. As a result, even for the low-resistance recording material S, it becomes possible to select an appropriate secondary transfer voltage that can achieve both suppression of image defects ("boss") due to insufficient transfer voltage and suppression of image defects ("burn-through") due to excessive transfer voltage.

[0080] Here, when one chart 100 is formed on one sheet of recording material S, the step width of the secondary transfer voltage is changed while the one sheet of recording material S forming the chart 100 passes through the secondary transfer unit N2. Also, when one (one set) of charts 100 is formed by dividing it among a plurality of sheets of recording material S, the step width of the secondary transfer voltage may be changed while any one of the recording materials S passes through the secondary transfer unit N2, or may be changed during the period corresponding to between the recording materials S.

[0081] Note that, for example, a configuration can be considered in which an operator selects the setting of the step width of the secondary transfer voltage at the time of forming the chart 100 according to the type and state of the recording material S used for image formation, according to this embodiment. For example, the setting of the step width in each of the cases of the above-mentioned normal recording material S, high-resistance recording material S, and low-resistance recording material S can be made selectable at the operation unit 70 or the external device 200. However, when executing the adjustment mode, it is often difficult for the operator to accurately predict the states of various recording materials S and manually set the step width of the secondary transfer voltage at the time of forming the chart 100 appropriately.

[0082] Therefore, in this embodiment, the control unit 30 is configured to automatically select the setting of the step width in each of the cases of the above-mentioned normal recording material S, high-resistance recording material S, and low-resistance recording material S, based on the detection result of the current detection sensor 76b at the time of forming the chart 100.

[0083] Note that, in the example shown in FIG. 9, corresponding to the method of automatically selecting the step width in this embodiment, which will be described in detail later, in both cases of the high-resistance recording material S and the low-resistance recording material S, the step width on the higher voltage side was changed with respect to the step width on the lower voltage side. However, in a configuration such as a configuration in which information regarding the electrical resistance of the recording material S is acquired by the method of Example 2 described later and the setting of the step width is selected, the mode of change of this step width may be different from the above.

[0084] Here, in the case of the high-resistance recording material S, from the viewpoint of reaching an appropriate transfer voltage within one chart as described above, it can be said that it is preferable to make the step width on the higher-voltage side larger than the step width on the lower-voltage side as in the above example. Therefore, in the configuration where the absolute value of the test voltage is increased step by step when forming the chart as in the above example, in the case of the high-resistance recording material S, it can be said that it is preferable to make the voltage on the last (maximum) adjustment value side larger than the step width on the first (minimum) adjustment value side. Also, in the case of the low-resistance recording material S, from the viewpoint of preventing the step of the transfer voltage from becoming too coarse in the vicinity of the appropriate transfer voltage as described above, it can be said that it is preferable to make the step width on the lower-voltage side smaller than the step width on the higher-voltage side. Therefore, in the configuration where the absolute value of the test voltage is increased step by step when forming the chart as in the above example, in the case of the low-resistance recording material S, conversely to the above example, it can be said that it is preferable to make the step width on the first (minimum) adjustment value side smaller than the voltage on the last (maximum) adjustment value side.

[0085] On the other hand, in a configuration where the absolute value of the test voltage is decreased step by step when forming the chart, which is different from the above example, in the case of the high-resistance recording material S, it can be said that it is preferable to make the step width on the first (minimum) adjustment value side larger than the step width on the last (maximum) adjustment value side. In this case, at the same time, the absolute value of the test voltage corresponding to the first (minimum) adjustment value may be made as large as the test voltage corresponding to the last (maximum) adjustment value in the above example. Also, in a configuration where the absolute value of the test voltage is decreased step by step when forming the chart, which is different from the above example, in the case of the low-resistance recording material S, it can be said that it is preferable to make the step width on the last (maximum) adjustment value side smaller than the step width on the first (minimum) adjustment value side, similar to the above example.

[0086] 5-3. Procedure of the operation of the adjustment mode of this embodiment Next, the operation of the adjustment mode in this embodiment will be described in more detail. FIG. 10 is a flowchart showing an outline of the procedure of the adjustment mode in this embodiment. Further, FIG. 11 is a schematic diagram showing an example of a setting screen for the adjustment mode. As described above, in this embodiment, the image forming apparatus 1 applies the secondary transfer voltage under constant voltage control, and the current at that time is detected by the current detection sensor 76b. Further, in this embodiment, in the case of a normal recording material S, during the formation of one chart 100, the secondary transfer voltage is sequentially increased in a substantially constant step width of 150V. Further, in this embodiment, the image forming apparatus 1 reads the luminance value of the blue-veta patch of the chart 100 by the reading device 80, and determines the recommended adjustment value of the secondary transfer voltage. Here, the case of forming the large chart 100L as described above as the chart 100 is taken as an example. Here, the case where the operator inputs an instruction from the operation unit 70 of the image forming apparatus 1 to execute the adjustment mode is taken as an example. For simplicity, the recording material on which the chart is formed may be simply referred to as "chart".

[0087] The setting screen for the adjustment mode will be described. In this embodiment, the control unit 30 (adjustment process unit 31d) causes the display unit 70a of the operation unit 70 to display a setting screen 300 for the adjustment mode as shown in FIG. 11. The setting screen 300 has a voltage setting unit 301 for setting adjustment values of the secondary transfer voltage for the front side (first side) and the back side (second side) of the recording material S. Further, the setting screen 300 has an output surface selection unit 302 for selecting whether to output the chart 100 on one side or both sides of the recording material S. Further, the setting screen 300 has an output instruction unit (chart output button) 303 for instructing the output of the chart 100. Further, the setting screen 300 has a confirmation unit (OK button) 304 for confirming the setting and a cancel button 305 for canceling the change of the setting. The control unit 30 (adjustment process unit 31d) can acquire information regarding various settings input via the setting screen 300 at the operation unit 70 and store it in the storage unit (RAM 33, secondary transfer voltage storage unit / calculation unit 31f, etc.) as necessary.

[0088] In this embodiment, before the output of the chart 100, the adjustment value displayed on the voltage setting unit 301 indicates the center voltage value (the value corresponding to the "0" patch of the chart) of the secondary transfer voltage (more specifically, the recording material share voltage Vp) when forming the chart 100 for the normal recording material S. When the adjustment value "0" is selected on the voltage setting unit 301 and the chart 100 is output, in the case of the normal recording material S, the above center voltage value is set to a specified value (table value) preset for the currently selected recording material S. The adjustment value displayed on this voltage setting unit 301 can be changed by the operator. When an adjustment value other than "0" is selected and the chart 100 is output, in the case of the normal recording material S, the center voltage value is changed by an adjustment amount ΔV of 150 V for each level of the adjustment value, and the chart 100 is output. As will be described in detail later, in this embodiment, the control unit 30 (adjustment process unit 31d) can change the step width of the secondary transfer voltage during the formation of the chart 100. Therefore, when the step width of the secondary transfer voltage is changed in this way, the secondary transfer voltage corresponding to the adjustment value "0" is changed from the secondary transfer voltage in the case of the normal recording material S. Also, when the chart output button 303 is operated, the chart 100 is output. And in this embodiment, after the output of the chart 100, the voltage setting unit 301 displays the recommended adjustment value of the secondary transfer voltage determined by the control unit 30 based on the reading result by the chart reading device 80 of the chart 100. The adjustment value displayed on this voltage setting unit 301 can be changed by the operator. When the OK button 104 is operated in a state where the adjustment value determined by the control unit 30 or the adjustment value changed by the operator is selected on the voltage setting unit 301, the adjustment value of the secondary transfer voltage is determined.

[0089] Note that before the output of the chart 100, the adjustment value displayed on the voltage setting unit 301 may be set to indicate the currently set adjustment value for the currently selected recording material S. Also, before the output of the chart 100, on the setting screen 300, a secondary transfer voltage other than the center voltage value, for example, the secondary transfer voltage of the first (minimum) adjustment value (for example, the adjustment value -5 of the large chart 100L) when forming the chart 100, may be set.

[0090] The procedure of the adjustment mode will be described. First, when information on the recording material S (paper type category, size, etc.) used in the adjustment mode is input by the operator, the control unit 30 (adjustment process unit 31d) causes the display unit 70a to display the setting screen 300 for the adjustment mode (S201). For example, the control unit 30 (adjustment process unit 31d) causes the setting screen 300 to be displayed on the display unit 70a in response to an operation of a button or the like provided on the input screen for the information of the recording material S displayed on the display unit 70a to call the setting screen 300 for the adjustment mode. The control unit 30 (adjustment process unit 31d) acquires the information of the recording material S input by the operator on the input screen, and adjusts the secondary transfer voltage in association with the information of the recording material S. Note that the information of the recording material S may be acquired from information that is set in advance in association with the recording material cassette 91 in which the recording material S used in the adjustment mode is stored when the recording material cassette 91 is selected.

[0091] Next, the control unit 30 (adjustment process unit 31d) acquires information on the setting of the center voltage value of the secondary transfer voltage during the formation of the chart 100 and the setting of whether to output a single-sided chart or a double-sided chart, which is input by the operator on the setting screen 300 (S202). As described above, in this embodiment, the center voltage value corresponds to the center voltage value in the case of the normal recording material S. Next, the control unit 30 (adjustment process unit 31d) acquires a signal indicating that the operator has operated the chart output button 303 on the setting screen 300 (S203). Then, prior to the output of the chart 100, the control unit 30 (adjustment process unit 31d) acquires a polynomial of the second degree or higher (a quadratic equation in this embodiment) of the relationship between the voltage and the current corresponding to the low electrical resistance of the secondary transfer unit N2 by the same operation as the aforementioned ATVC control (S204). Then, the control unit 30 (adjustment process unit 31d) sets the secondary transfer voltage (test voltage) based on the acquired information on the relationship between the voltage and the current and the information on the center voltage value set on the setting screen 300, and controls to start the output of the chart 100 (S205). At this time, the control unit 30 (adjustment process unit 31d) adjusts the image data of the chart 100 according to the size of the recording material S as described above, and first controls to output the chart 100 while changing the secondary transfer voltage every 150V. Here, since the case of outputting the large chart 100L is taken as an example, the control unit 30 (adjustment process unit 31d) controls to output the chart 100 having 11 sets of patch sets as described above.

[0092] Next, the control unit 30 (adjustment process unit 31d) detects the voltage and the current when applying the secondary transfer voltages of the adjustment values -5, -4, and -3 by the voltage detection sensor 76a and the current detection sensor 76b (S206). Note that the voltage value may be detected (recognized) from the output instruction value for the secondary transfer power supply 76. Next, the control unit 30 (adjustment process unit 31d) calculates the slope of the voltage-current characteristic based on the detection results of the voltage and the current when applying the secondary transfer voltages of the adjustment values -5, -4, and -3 (S207).

[0093] Next, the control unit (adjustment process unit 31d) determines whether the slope (absolute value) of the voltage-current characteristic calculated in S207 is equal to or less than a predetermined lower limit threshold value (S208). This lower limit threshold value is preset according to the electrical resistance of the recording material S for which it is desirable to change the step width of the secondary transfer voltage during the formation of the chart 100 in order to make the adjustable range of the secondary transfer voltage sufficient, and is stored in advance in the ROM 32. The recording material S with the slope equal to or less than the lower limit threshold value corresponds to a high-resistance recording material S having a higher electrical resistance than the normal recording material S. Then, when the control unit 30 (adjustment process unit 31d) determines in S208 that the slope is equal to or less than the lower limit threshold value, it controls the step width of the secondary transfer voltage after adjustment value -3 to increase from 150V to 300V (S209). That is, the step width of the secondary transfer voltage between adjustment value -3 and adjustment value -2 and between subsequent adjustment values is set to 300V.

[0094] Also, when the control unit 30 (adjustment process unit 31d) determines in S208 that the slope is not less than (greater than) the lower limit threshold value, it determines whether the slope is equal to or greater than a predetermined upper limit threshold value (S210). This upper limit threshold value is preset according to the electrical resistance of the recording material S for which it is desirable to change the step width of the secondary transfer voltage during the formation of the chart 100 in order to prevent the step of the secondary transfer voltage from becoming too coarse, and is stored in advance in the ROM 32. The recording material S with the slope equal to or greater than the upper limit threshold value corresponds to a low-resistance recording material S having a lower electrical resistance than the normal recording material S. Then, when the control unit 30 (adjustment process unit 31d) determines in S210 that the slope is equal to or greater than the upper limit threshold value, it controls the step width of the secondary transfer voltage after adjustment value -3 to decrease from 150V to 75V (S211). That is, the step width of the secondary transfer voltage between adjustment value -3 and adjustment value -2 and between subsequent adjustment values is set to 75V.

[0095] Furthermore, when the control unit 30 (adjustment process unit 31d) determines in S210 that the above-mentioned slope is not greater than the upper limit threshold value (greater than the lower limit threshold value and less than the upper limit threshold value), it proceeds as follows. That is, during the formation of the chart 100, control is performed so as not to change the step width of the secondary transfer voltage from 150V (S212). The recording material S with a slope greater than the lower limit threshold value and less than the upper limit threshold value corresponds to a normal recording material S having a standard electrical resistance based on the type of the recording material S and the like.

[0096] The control unit 30 (adjustment process unit 31d) performs the above-mentioned calculation of the slope and the selection of the setting of the step width of the secondary transfer voltage when switching the secondary transfer voltage from the adjustment value -3 to the adjustment value -2 during the formation of the chart 100.

[0097] Thereafter, the control unit 30 (adjustment process unit 31d) transfers the remaining patch sets (adjustment values -2, -1, 0, +1, +2, +3, +4, +5) to the recording material S while changing the secondary transfer voltage with the step width set in S209, S211, or S212, and ends the output of the chart 100 (S213).

[0098] Next, the output chart 100 is set by the operator in the reading device 80, read by the reading device 80, and the information of the chart 100 including the luminance information (density information) of each blue beta patch is input to the control unit 30 (adjustment process unit 31d) (S214). At this time, the control unit 30 (adjustment process unit 31d) can display on the setting screen 300 a prompt for the operator to set the chart 100 in the reading device 80. Also, the control unit 30 (adjustment process unit 31d) can start the reading of the chart 100 when the operator operates the start button (not shown) on the operation unit 70. Next, the control unit 30 (adjustment process unit 31d) determines the recommended adjustment value of the secondary transfer voltage and displays it on the voltage setting unit 301 of the setting screen 300 (S215). An example of the process for determining the recommended adjustment value of this secondary transfer voltage will be described later.

[0099] The adjustment value displayed in the voltage setting unit 301 of the setting screen 300 at S215 indicates a candidate for a preferable setting of the secondary transfer voltage. The operator can visually check the chart 100 or the like and determine whether the adjustment value displayed on the setting screen 300 is appropriate. If the operator does not change the adjustment value displayed on the setting screen 300, the operator operates the OK button 304 on the setting screen 300 as it is. On the other hand, when the operator changes (manually adjusts) the adjustment value displayed on the setting screen 300, the operator inputs the adjustment value to be set in the voltage setting unit 301 of the setting screen 300 and operates the OK button 304 on the setting screen 300. Therefore, the control unit 30 (adjustment process unit 31d) determines whether or not the adjustment value has been changed (S216). Then, when the control unit 30 (adjustment process unit 31d) obtains a signal indicating that the OK button 304 has been operated without changing the adjustment value, the control unit stores the adjustment value determined at S215 in the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f) (S217). On the other hand, when the control unit 30 (adjustment process unit 31d) obtains a signal indicating that the OK button 304 has been operated after the adjustment value has been changed, the control unit stores the adjustment value input by the operator in the RAM 33 (or the secondary transfer voltage storage unit / calculation unit 31f) (S218). Note that the adjustment amount ΔV obtained as described later may be stored. The adjustment mode ends here.

[0100] When the control unit 30 (secondary transfer voltage memory unit / calculation unit 31f) executes a subsequent job after using the recording material S for which the secondary transfer voltage has been set in the adjustment mode, it sets the secondary transfer voltage according to the adjustment value stored as described above until the adjustment mode is executed next. That is, the control unit 30 (secondary transfer voltage memory unit / calculation unit 31f) calculates the adjustment amount ΔV based on the adjustment value stored as described above and the step width of the secondary transfer voltage that has or has not been changed during the formation of the chart 100. When the step width of the secondary transfer voltage has not been changed during the formation of the chart 100, this adjustment amount ΔV can be calculated as ΔV = adjustment value × 150V. When the step width of the secondary transfer voltage has been changed during the formation of the chart 100, the adjustment amount ΔV can be calculated in accordance with the above based on the adjustment value stored as described above and the step widths before and after the change. Then, the control unit 30 (secondary transfer voltage memory unit / calculation unit 31f) calculates the adjusted recording material shared voltage Vp + ΔV using the calculated adjustment amount ΔV, and calculates the secondary transfer voltage Vtr (= Vb + Vp + ΔV) using this adjusted recording material shared voltage Vp + ΔV.

[0101] Here, an example of the process for determining the recommended adjustment value of the secondary transfer voltage in S215 will be described. The control unit 30 (adjustment process unit 31d) acquires the RGB luminance data (8 bits) of the blue beta patches corresponding to each adjustment value (-5 to 0 to +5), which is read from the chart 100 and stored in the RAM 33. Next, the control unit 30 (adjustment process unit 31d) calculates the average luminance value of each patch using the acquired luminance data. As a result, information indicating the relationship between the adjustment value (secondary transfer voltage) and the average luminance value of the patch as shown in FIGS. 9(a) and 9(b) is obtained. Next, the control unit 30 (adjustment process unit 31d) sequentially calculates the standard deviation of the average luminance value for every predetermined number of patches, for example, from patches with a small adjustment value to patches with a large adjustment value. Then, the control unit 30 (adjustment process unit 31d) extracts the adjustment value at which the standard deviation of the average luminance value is minimized. Further, the control unit 30 (adjustment process unit 31d) selects the maximum adjustment value among the adjustment values for which the recording material shared voltage Vp + ΔV (absolute value) determined from the extracted adjustment values is equal to or less than a predetermined upper limit value. That is, within the range where the recording material shared voltage Vp + ΔV does not exceed the upper limit value, the adjustment value at which the average luminance value of the blue beta patch is minimized (the density is maximized) is selected. Note that the above upper limit value is preset according to, for example, the paper type category of the recording material S, from the viewpoint of suppressing image defects due to the secondary transfer voltage being too high. Then, the control unit 30 (adjustment process unit 31d) determines the selected adjustment value as the recommended adjustment value of the secondary transfer voltage and stores it in the RAM 33. Through such processing, the adjustment value at around which the decrease in the average luminance value (increase in density) saturates is determined as the recommended adjustment value.

[0102] Note that the method for determining the recommended adjustment value of the secondary transfer voltage is not limited to the method described above. For example, the adjustment amount of the secondary transfer voltage may be determined based on extracting the adjustment value in the luminance stable region where the luminance difference between adjacent adjustment values is equal to or less than a predetermined value, or the adjustment value at which the average luminance value is minimized (the density is maximized).

[0103] Referring to FIGS. 8 and 9 again, in this embodiment, when the slope of the voltage-current characteristic when applying the secondary transfer voltages of adjustment values -5, -4, and -3 is equal to or less than the lower threshold value as shown in FIG. 8(a), the following is done. That is, as shown in FIG. 9(a), the step width of the secondary transfer voltage is increased from 150 V to 300 V to form the remaining patches (adjustment values -2, -1, 0, +1, +2, +3, +4, +5). Thereby, even in the case of the recording material S of high-resistance paper where the above slope is smaller than that of the normal recording material S, the step width can be automatically changed to obtain an appropriate adjustment amount of the secondary transfer voltage. Also, in this embodiment, when the slope of the voltage-current characteristic when applying the secondary transfer voltages of adjustment values -5, -4, and -3 is equal to or greater than the upper threshold value as shown in FIG. 8(a), the following is done. That is, as shown in FIG. 9(b), the step width of the secondary transfer voltage is decreased from 150 V to 75 V to form the remaining patches (adjustment values -2, -1, 0, +1, +2, +3, +4, +5). Thereby, even in the case of the recording material S of low resistance where the above slope is larger than that of the normal recording material S, the step width can be automatically changed to obtain an appropriate adjustment amount of the secondary transfer voltage that can achieve both suppression of "boso" and suppression of "breaking through".

[0104] In this embodiment, the control unit 30 automatically controls the setting of the step width of the secondary transfer voltage based on the detection result of the voltage-current characteristics when forming the chart 100. Thereby, while reducing the operation burden on the operator, it becomes possible to more appropriately control the setting of the step width of the secondary transfer voltage according to the type and state of the recording material S. In particular, in this embodiment, information regarding the electrical resistance of the recording material S was obtained based on the slope of the voltage-current characteristics obtained by applying three levels of secondary transfer voltage (test voltage). Thereby, it is possible to obtain information regarding the electrical resistance of the recording material S with higher accuracy. However, information regarding the electrical resistance of the recording material S can be obtained based on the detection result of the current value (or voltage value) obtained by applying at least one secondary transfer voltage (test voltage). For example, information regarding the electrical resistance of the recording material S can be obtained based on the slope of the voltage-current characteristics obtained by applying two levels of secondary transfer voltage (test voltage) or the difference in the detection results of two levels of current values (or voltage values). Further, based on the detection result of a single level of current value (or voltage value), information regarding the electrical resistance of the recording material S can be obtained from its absolute value, the difference from the zero point, or the slope of the voltage-current characteristics subtracted from the zero point, etc.

[0105] As described above, in this embodiment, the image forming apparatus 1 includes an image carrier 44b that carries a toner image, a transfer member 45b that forms a transfer unit N2 that abuts against the image carrier 44b and transfers the toner image from the image carrier 44b to a recording material S, an application unit 76 that applies a voltage to the transfer member 45b, a detection unit 76b that detects a voltage value or a current value when the application unit 76 applies a voltage to the transfer member 45b, a control unit 30 that is in an adjustment mode for adjusting a transfer voltage applied to the transfer member 45b by the application unit 76 during transfer of the toner image, and forms a chart 100 on the recording material S by applying a plurality of test voltages to the transfer member 45b by the application unit 76 to transfer a plurality of test images, and is capable of executing an adjustment mode in which the test voltage is changed so that the absolute value of the test voltage is increased or decreased step by step. In this embodiment, the image carrier 44b is an intermediate transfer body that conveys a toner image transferred from another image carrier to transfer it to the recording material S by the transfer unit N2. And in this embodiment, the control unit 30 can change the change width (step width) in one step of the test voltage applied during the formation of the chart 100 based on the detection result of the detection unit 76b when a voltage is applied to the transfer member 45b when the recording material S forming the chart 100 is at the transfer unit N2. In this embodiment, the control unit 30 can change the change width based on the detection result of the detection unit 76b when at least one test voltage is applied during the formation of the chart 100. The control unit 30 can change so as to increase the change width during the formation of the chart 100 when the detection result of the detection unit 76b indicates that the electrical resistance of the recording material S at the transfer unit N2 is equal to or greater than a predetermined value. Further, the control unit 30 can change so as to decrease the change width during the formation of the chart 100 when the detection result of the detection unit 76b indicates that the electrical resistance of the recording material S at the transfer unit N2 is equal to or less than a predetermined value. Further, the control unit 30 can change the change width during the formation of the chart based on the slope of the voltage-current characteristic based on the detection result of the detection unit 76b when at least two test voltages are applied during the formation of the chart 100. In this case, the control unit 30 can change so as to increase the change width during the formation of the chart 100 when the absolute value of the slope is equal to or less than a predetermined value.Also, in this case, when the absolute value of the above inclination is equal to or greater than a predetermined value, the control unit 30 can change the above change width to be smaller during the formation of the chart 100.

[0106] Also, in this embodiment, it has a reading means 80 for acquiring information regarding the density of the test image of the chart 100, and the control unit 30 outputs information regarding the adjustment amount of the transfer voltage based on the information regarding the density of the test image of the chart 100 acquired by the reading means 80. Here, the chart 100 may be formed on one surface of a single recording material S or separately formed on one surface of each of a plurality of recording materials S.

[0107] As described above, according to this embodiment, the step width of the secondary transfer voltage can be changed during the formation of the chart 100. Thus, it is possible to suppress the situation where the adjustable range of the secondary transfer voltage becomes narrower than the required range in the case of a high-resistance recording material S, or the situation where it becomes difficult to adjust to an appropriate secondary transfer voltage because the step of the secondary transfer voltage is coarse in the case of a low-resistance recording material S. Also, according to this embodiment, based on the detection result of the current detection sensor 76b, the step width of the secondary transfer voltage at the time of forming the chart can be automatically changed. Thereby, the operator can easily and appropriately adjust the step width without manually adjusting the step width of the secondary transfer voltage at the time of forming the chart 100. That is, according to this embodiment, it is possible to easily and appropriately set the change width in one step of the test voltage at the time of forming the chart 100 according to the recording material S and appropriately adjust the secondary transfer voltage. Thus, this embodiment is effective in improving the usability of the image forming apparatus 1 and improving media compatibility.

[0108] [Embodiment 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 denoted by the same reference numerals as in Embodiment 1, and detailed description thereof is omitted.

[0109] In this embodiment, when the chart 100 is output, before transferring the patch to the recording material S, the image forming apparatus 1 can acquire information regarding the electrical resistance of the recording material S and can globally change the step width of the secondary transfer voltage during the formation of the chart 100.

[0110] FIG. 12 is a graph showing changes in the current detected by the current detection sensor 76b before and after the recording material S enters the secondary transfer unit N2 when the chart 100 is output, for explaining the operation of the adjustment mode of this embodiment. In FIGS. 12(a) and 12(b), the horizontal axis represents time and the vertical axis represents current. FIG. 12(a) shows the case of the recording material S with high resistance, and FIG. 12(b) shows the case of the recording material S with low resistance.

[0111] Similar to the first embodiment, in this embodiment, the image forming apparatus 1 is configured to apply the secondary transfer voltage under constant voltage control and detect the current at that time with the current detection sensor (current detection circuit) 76b. However, the present invention is not limited to such a configuration, and the image forming apparatus 1 may be configured to apply the secondary transfer voltage under constant current control and detect the voltage at that time with the voltage detection sensor (voltage detection circuit) 76a.

[0112] In this embodiment, when outputting the chart 100, a predetermined voltage is applied to the secondary transfer roller 45b by constant voltage control before the recording material S enters the secondary transfer unit N2, and the current at that time is detected by the current detection sensor 76b. As a result, information on the transition of the current as shown in FIG. 12 is obtained. The current value before the leading end of the recording material (paper) S in the conveyance direction that forms the chart 100 enters the secondary transfer unit N2 fluctuates due to non-uniform electrical resistance in the circumferential direction of the secondary transfer roller 45b, but is mainly determined by the electrical resistance of the secondary transfer roller 45b. Then, when the leading end of the recording material S in the conveyance direction enters the secondary transfer unit N2, the electrical resistance of the recording material S is added, and the current value decreases. The amount of decrease in this current value (hereinafter also referred to as "current decrease amount") varies depending on the electrical resistance of the recording material S. Therefore, as shown in FIG. 12(a), in the case of a recording material S with high resistance or a recording material S left in an environment (such as NL (normal temperature and low humidity environment)) where the electrical resistance of the recording material S becomes high, the above-mentioned current decrease amount becomes large. On the other hand, as shown in FIG. 12(b), in the case of a recording material S with low resistance or a recording material S left in an environment (such as HH (high temperature and high humidity environment)) where the electrical resistance of the recording material S becomes low, the above-mentioned current decrease amount becomes small.

[0113] In this way, based on the detection result of the current detection sensor 76b, it is possible to detect the amount of current decrease caused by the leading end of the recording material S in the conveyance direction entering the secondary transfer portion N2. Then, according to this amount of current decrease, the step width of the secondary transfer voltage at the time of forming the chart 100 can be changed. Specifically, in this embodiment, when the amount of current decrease is neither greater than nor less than a certain value, assuming that the recording material S has a standard electrical resistance based on its type or the like, the step width of the secondary transfer voltage at the time of forming the chart 100 is set to 150V. When the amount of current decrease is greater than or equal to a certain value, since the electrical resistance of the recording material S is large, the step width of the secondary transfer voltage at the time of forming the chart 100 is changed to be increased from 150V to 300V. On the other hand, when the amount of current decrease is less than or equal to a certain value, since the electrical resistance of the recording material S is small, the step width of the secondary transfer voltage at the time of forming the chart 100 is changed to be decreased from 150V to 75V. In this way, in this embodiment, based on the amount of current decrease, the step width of the secondary transfer voltage during the formation of one chart 100 is changed as a whole.

[0114] Note that information regarding the electrical resistance of the recording material S forming the chart 100 can be obtained with higher accuracy by being acquired based on the amount of current decrease obtained from the difference in current values before and after the leading end of the recording material S in the conveyance direction enters the secondary transfer unit N2. However, it is not limited to this, and it may be determined based on, for example, the ratio of one detection result to the other detection result among the detection results of the current value (or voltage value) before and after the leading end of the recording material S in the conveyance direction enters the secondary transfer unit N2. Further, information regarding the electrical resistance of the recording material S forming the chart 100 can be obtained from the detection result of at least one current value from when the recording material S enters the secondary transfer unit N2 until the first patch is transferred. For example, the method similar to that of Example 1 may be applied to obtain information regarding the electrical resistance of the recording material S. In this case, information regarding the electrical resistance of the recording material S can be obtained based on the detection results of current values at a plurality of levels from when the recording material S enters the secondary transfer unit N2 until the first patch is transferred. That is, similar to what was described in Example 1, information regarding the electrical resistance of the recording material S can be obtained based on the detection result of the current value (or voltage value) at one point or a plurality of points when the recording material S is in the secondary transfer unit N2. For example, information regarding the electrical resistance of the recording material S can be obtained based on the slope of the voltage-current characteristics obtained from the detection results of current values (or voltage values) at a plurality of levels such as two levels and three levels. Further, for example, information regarding the electrical resistance of the recording material S can be obtained based on the difference in the detection results of current values (or voltage values) at two levels. Further, for example, based on the detection result of the current value (or voltage value) at one level, information regarding the electrical resistance of the recording material S can be obtained from its absolute value, the difference from the zero point, or the slope of the voltage-current characteristics subtracted by the zero point.

[0115] Further, the predetermined voltage applied to the secondary transfer roller 45b to obtain information regarding the electrical resistance of the recording material S forming the chart 100 may be the same as any of the secondary transfer voltages (test voltages) during the formation of the chart 100, or may be different.

[0116] Also, when the chart 100 is formed separately on a plurality of recording materials S, information regarding the electrical resistance of the first recording material S may be acquired. However, when the chart 100 is formed separately on a plurality of recording materials S, information regarding the electrical resistance of a plurality of (all may be acceptable) recording materials S may be acquired. In this case, regarding the test image formed on the recording material S for which information regarding the electrical resistance has been acquired, the step width of the secondary transfer voltage can be determined based on the acquired information.

[0117] Next, the operation of the adjustment mode in this embodiment will be described in more detail. FIG. 13 is a flowchart showing an outline of the procedure of the adjustment mode in this embodiment. As described above, in this embodiment, the image forming apparatus 1 applies a secondary transfer voltage under constant voltage control and detects the current at that time with the current detection sensor 76b. Also, in the procedure of FIG. 13, descriptions of processes similar to those in the procedure of FIG. 10 described in the first embodiment will be omitted as appropriate.

[0118] The processes of S301 to S305 in FIG. 13 are the same as the processes of S201 to S205 in FIG. 10 described in the first embodiment.

[0119] Next, the control unit 30 (adjustment process unit 31d) detects, using the current detection sensor 76b, the current values before and after the leading end of the recording material S forming the chart 100 enters the secondary transfer unit N2 (S306). Thereby, information on the transition of the current as shown in FIG. 12 is acquired. Next, the control unit 30 (adjustment process unit 31d) calculates the amount of current decrease from the difference between the current values before and after the leading end of the recording material S in the conveyance direction enters the secondary transfer unit N2 (S307). For example, the control unit 30 (adjustment process unit 31d) can calculate the amount of current decrease from the difference between the current value a predetermined time before the leading end of the recording material S reaches the secondary transfer unit N2 and the current value a predetermined time after reaching (within the period corresponding to the margin). The detection timing before the above arrival is preferably a timing at which a value reflecting the electrical resistance of the secondary transfer unit N2, which is mainly the electrical resistance of the secondary transfer roller 45b, can be stably detected. Also, the detection timing after the above arrival is preferably a timing at which a value reflecting the electrical resistance of the secondary transfer unit N2 to which the electrical resistance of the recording material S is added can be stably detected.

[0120] Next, the control unit 30 (adjustment process unit 31d) determines whether or not the amount of current decrease calculated in S307 is equal to or greater than a predetermined upper limit threshold value (S308). This upper limit threshold value is preset according to the electrical resistance of the recording material S and the like, which is desired to make the step width of the secondary transfer voltage different from that in the case of a normal recording material S in order to make the adjustable range of the secondary transfer voltage sufficient, and is stored in advance in the ROM 32. The recording material S with the amount of current decrease equal to or greater than the upper limit threshold value corresponds to a high-resistance recording material S having a higher electrical resistance than a normal recording material S. Then, when the control unit 30 determines in S308 that the amount of current decrease is equal to or greater than the upper limit threshold value, it controls so that the step width of the secondary transfer voltage at the time of forming the chart 100 is set to 300V, which is greater than 150V in the case of a normal recording material S (S309).

[0121] Further, when the control unit 30 (adjustment process unit 31d) determines in S308 that the amount of current decrease is not greater than the upper limit threshold (less than the upper limit threshold), it determines whether the amount of current decrease is less than or equal to a predetermined lower limit threshold (S310). This lower limit threshold is preset according to the electrical resistance of the recording material S, etc., which is desired to make the step width of the secondary transfer voltage different from that in the case of the normal recording material S so that the step of the secondary transfer voltage does not become too coarse, and is stored in advance in the ROM 32. The recording material S with the amount of current decrease less than or equal to the lower limit threshold corresponds to a low-resistance recording material S having a lower electrical resistance than the normal recording material S. Then, when the control unit 30 determines in S310 that the amount of current decrease is less than or equal to the lower limit threshold, it controls the step width of the secondary transfer voltage at the time of forming the chart 100 to be 75V, which is smaller than 150V in the case of the normal recording material S (S311).

[0122] Furthermore, when the control unit 30 (adjustment process unit 31d) determines in S310 that the amount of current decrease is not less than the lower limit threshold (greater than the lower limit threshold and less than the upper limit threshold), it proceeds as follows. That is, it controls the step width of the secondary transfer voltage at the time of forming the chart 100 not to be changed from 150V in the case of the normal recording material S (S312). The recording material S with the amount of current decrease greater than the lower limit threshold and less than the upper limit threshold corresponds to a normal recording material S having a standard electrical resistance based on the type of the recording material S, etc.

[0123] The control unit 30 (adjustment process unit 31d) performs the calculation of the above-described amount of current decrease and the selection of the setting of the step width of the secondary transfer voltage before starting the transfer of the first patch of the recording material S with the secondary transfer voltage of the first adjustment value when outputting the chart 100.

[0124] Thereafter, the control unit 30 (adjustment process unit 31d) changes the secondary transfer voltage with the step width set in S309, S311, or S312, transfers all the patch sets (adjustment values -5, -4, -3, -2, -1, 0, +1, +2, +3, +4, +5) to the recording material S, and ends the output of the chart 100 (S313).

[0125] The processes of S314 to S318 in FIG. 13 are the same as the processes of S214 to S218 in FIG. 10 described in the first embodiment.

[0126] In this embodiment, when the amount of current decrease due to the leading end of the recording material S forming the chart 100 entering the secondary transfer unit N2 is equal to or less than the lower threshold value, the step width of all the secondary transfer voltages during the formation of the chart 100 is increased from 150V to 300V in the case of a normal recording material S. Thereby, even in the case of a recording material S of high-resistance paper, the step width can be automatically changed to obtain an appropriate adjustment amount of the secondary transfer voltage. Further, in this embodiment, when the amount of current decrease is equal to or greater than the upper threshold value, the step width of all the secondary transfer voltages during the formation of the chart 100 is decreased from 150V to 75V in the case of a normal recording material S. Thereby, even in the case of a recording material S of low resistance, the step width can be automatically changed to obtain an appropriate adjustment amount of the secondary transfer voltage that can achieve both suppression of "bossing" and suppression of "penetration".

[0127] Note that information regarding the electrical resistance of the recording material S may be acquired in the same manner as in this embodiment, and based on the result, the step width of the secondary transfer voltage may be changed during the formation of the chart 100 in the same manner as described in the first embodiment.

[0128] As described above, in this embodiment, the control unit 30 can change the change width (step width) in one stage of the test voltage applied during the formation of the chart 100 based on the detection result of the detection unit 76b when a voltage is applied to the transfer member 45b when the recording material S forming the chart 100 is at the transfer unit N2. In this embodiment, the control unit 30 determines the above change width based on the detection result of the detection unit 76b when the recording material S forming the chart 100 is at the transfer unit N2 before performing the transfer of the test image that is first transferred to the recording material S among the plurality of test images of the chart 100. When the detection result of the detection unit 6b indicates that the electrical resistance of the recording material S at the transfer unit N2 is the first value, the control unit 30 sets the above change width as the first change width, and when the detection result of the detection unit 76b indicates that the electrical resistance of the recording material S at the transfer unit N2 is a second value greater than the first value, the control unit 30 can set the above change width as a second change width greater than the first change width. Further, the control unit 30 can determine the above change width during the formation of the chart 100 based on the first detection result of the detection unit 76b when the recording material S forming the chart 100 is not at the transfer unit N2 and the second detection result of the detection unit N2 when the recording material S forming the chart 100 is at the transfer unit N2 before performing the transfer of the test image that is first transferred to the recording material S among the plurality of test images of the chart 100. In this case, the control unit 30 can determine the above change width during the formation of the chart 100 based on the difference between the first detection result and the second detection result. Then, when the above difference is the first value, the control unit 30 sets the above change width as the first change width, and when the above difference is a second value greater than the first value, the control unit 30 can set the above change width as a second change width greater than the first change width.

[0129] As described above, according to this embodiment, without the operator manually adjusting, the step width of the secondary transfer voltage during the formation of the chart 100 can be easily and appropriately adjusted as a whole.

[0130] [Others] As described above, the present invention has been described with reference to specific embodiments, but the present invention is not limited to the above-described embodiments.

[0131] In the above-described embodiment, the luminance data was acquired using a blue patch. However, the color of the patch for acquiring the luminance data is not limited to blue, and secondary colors such as red and green or a solid color of YMCK may be used instead of blue. Also, halftone luminance data may be acquired.

[0132] Also, in the above-described embodiment, as the reading means, a reading device 80 that reads the chart 100 set by the operator as shown in FIG. 1 was used. However, the present invention is not limited to such an aspect, and as the reading means, a reading device that reads the chart 100 when the chart 100 is output from the image forming apparatus 1 may be used. For example, as shown in FIG. 14, an in-line image sensor 86 may be provided on the downstream side of the fixing unit 46 in the conveyance direction of the recording material S. In this case, when the chart 100 is output from the image forming apparatus 1, the chart 100 can be read by this image sensor 86 to acquire the density information (luminance information) of the patch.

[0133] Also, in the above-described embodiment, the control unit determined the recommended adjustment value of the secondary transfer voltage based on the result of reading the chart by the reading means. This is preferable because it is possible to reduce the operation burden on the operator. However, the present invention is not limited to such an aspect, and the operator may visually confirm the chart output in the adjustment mode or use a colorimeter to determine the adjustment value.

[0134] In the above-described embodiments, for each of the electrical resistances (normal, high resistance, low resistance) of the three-division recording material, a setting for the step width of the transfer voltage (test voltage) at the time of chart formation was provided. However, the present invention is not limited to such an aspect. For example, a setting for the step width of the transfer voltage (test voltage) at the time of chart formation may be provided for each of the electrical resistances of the two-division recording material, such as normal electrical resistance and high resistance, normal electrical resistance and low resistance, low resistance side and high resistance side. Further, a setting for the step width of the transfer voltage (test voltage) at the time of chart formation may be provided for each of the electrical resistances of the recording material having four or more divisions.

[0135] In the above-described embodiments, the secondary transfer voltage was adjusted using an adjustment value corresponding to a predetermined adjustment amount. However, for example, the adjustment amount may be directly set on a setting screen or the like.

[0136] In the above-described embodiments, the operations that were assumed to be performed by the operation unit of the image forming apparatus can be performed by an external device. That is, although the case where an operation by an operator is performed via the operation unit 70 of the image forming apparatus 1 and the adjustment mode is executed has been described, the operation may be performed via an external device 200 such as a personal computer, and the adjustment mode may be executed. In this case, the same settings as in the above-described embodiments can be made via the 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.

[0137] Although not described in the above-described embodiments, the detection result of the current and the detection result of the voltage may be, for example, the average value of a plurality of sampling values acquired at a predetermined sampling interval at one detection timing (for example, when applying a transfer voltage corresponding to a predetermined adjustment value).

[0138] When controlling the transfer voltage to a constant voltage, the voltage value may be detected (recognized) from the output instruction value for the power supply. When controlling the transfer voltage to a constant current, the current value may be detected (recognized) from the output instruction value for the power supply.

[0139] In addition, in the above-described embodiments, the configuration in which the secondary transfer voltage is controlled by a constant voltage has been described. However, the secondary transfer voltage may be controlled by a constant current. In the above-described embodiments, in the configuration in which the secondary transfer voltage is controlled by a constant voltage, the target voltage at the time of applying the secondary transfer voltage is adjusted by the adjustment mode to adjust the secondary transfer voltage. In the case of a configuration in which the secondary transfer voltage is controlled by a constant current, the secondary transfer voltage can be adjusted by adjusting the target current at the time of applying the secondary transfer voltage by the adjustment mode. The step width (change width in one step) of the transfer voltage (test voltage) includes not only the change width of the voltage value during constant voltage control but also the change width of the current value during constant current control.

[0140] In addition, the present invention is not limited to tandem-type image forming apparatuses, and can also be applied to other types of image forming apparatuses. Further, the image forming apparatus is not limited to a full-color image forming apparatus, and may be a monochrome or monocolor image forming apparatus. Further, the present invention can be implemented in various applications such as printers, various printing machines, copiers, FAX machines, and multifunction peripherals.

[0141] In addition, the present invention can be equally applied to, for example, a monochrome image forming apparatus having only one image forming unit. In this case, the present invention can be applied to a transfer unit in which a toner image is transferred from a photosensitive drum or the like as an image carrier directly onto a recording material.

Explanation of Reference Numerals

[0142] 30 Control unit 44b Intermediate transfer belt 45a Inner secondary transfer roller 45b Outer secondary transfer roller 46 Fixing unit 80 Reading device 100 Chart N2 Secondary transfer unit S Recording material

Claims

1. an image forming unit that forms a toner image; an image carrier that carries a toner image formed by the image forming unit; a transfer member forming a transfer section for transferring a toner image from the image carrier to a recording material; an application unit that applies a voltage to the transfer member; a detection unit that detects a voltage value or a current value when the application unit applies a voltage to the transfer member; a control unit configured to execute processing of a mode for outputting a chart formed by transferring a plurality of test toner images from the image carrier to a recording material in order to adjust a transfer voltage applied to the transfer member during image formation, the plurality of test toner images being formed by applying a plurality of different test voltages to the transfer member; having the plurality of test toner images include a first test toner image and a second test toner image, the first test toner image being transferred to a recording material by a first test voltage, and the second test toner image being transferred to a recording material by a second test voltage; an application unit that applies a voltage of a predetermined voltage value or a voltage that causes a current of a predetermined current value to flow through the transfer member to the transfer member when the recording material on which the chart is to be formed is in the transfer unit before the first test toner image and the second test toner image are formed, and corrects the first test voltage and the second test voltage so as to change a difference between the first test voltage and the second test voltage based on a detection result of a current value detected by the detection unit when a voltage of the predetermined voltage value is applied, or a detection result of a voltage value detected by the detection unit when a voltage that causes a current of the predetermined current value to flow through the transfer member is applied.

2. an image forming unit that forms a toner image; an image carrier that carries a toner image formed by the image forming unit; a transfer member forming a transfer section for transferring a toner image from the image carrier to a recording material; An application unit that applies a voltage to the transfer member; A detection unit that detects a voltage value or a current value when the application unit applies a voltage to the transfer member; A mode for outputting a chart formed by transferring a plurality of test toner images from the image carrier to a recording material in order to adjust a transfer voltage applied to the transfer member during image formation, wherein the plurality of test toner images are formed by applying a plurality of different test voltages to the transfer member. A control unit configured to execute a process of the mode; It has, The plurality of test toner images include a first test toner image and a second test toner image, the first test toner image is transferred to a recording material by a first test voltage, and the second test toner image is transferred to the recording material by a second test voltage. It is configured to be transferred, Before forming the first test toner image and the second test toner image, when the recording material on which the chart is formed is in the transfer unit, the application unit applies a first voltage of a predetermined first voltage value and a second voltage of a predetermined second voltage value to the transfer member, or a first voltage that causes a current of a predetermined first current value to flow through the transfer member and a second voltage that causes a current of a predetermined second current value to flow through the transfer member. Based on the first detection result of the current value detected by the detection unit when the first voltage of the first voltage value is applied and the second detection result of the current value detected by the detection unit when the second voltage of the second voltage value is applied, or the first detection result of the voltage value detected by the detection unit when the first voltage that causes the current of the first current value to flow through the transfer member is applied and the second detection result of the voltage value detected by the detection unit when the second voltage that causes the current of the second current value to flow through the transfer member is applied, the first test voltage and the second test voltage are corrected so as to change the difference between the first test voltage and the second test voltage. An image forming apparatus characterized by that.

3. The image forming apparatus according to claim 2, wherein the control unit sets the first test voltage and the second test voltage based on a difference between the first detection result and the second detection result. Claim 4 When the difference between the first detection result and the second detection result is equal to or less than a threshold value, the control unit sets the difference between the first test voltage and the second test voltage to be greater than a predetermined difference set based on the type of recording material on which the chart is formed. The image forming apparatus according to claim 3, characterized in that. Claim 5 When the difference between the first detection result and the second detection result exceeds a threshold value, the control unit sets the difference between the first test voltage and the second test voltage to be smaller than a predetermined difference set based on the type of recording material on which the chart is formed. The image forming apparatus according to claim 3, characterized in that.

Images