Image forming device

Abstract

To enable a transfer voltage to be easily adjusted, while mitigating the work load of operators and reducing unusable sheets of paper.SOLUTION: An image forming device comprises: an image carrier; a transfer member; an application unit; a feeding unit; a detection unit for detecting from a recording medium an index correlated with the type of recording medium on upstream from a transfer unit; a control unit for controlling a first operation to acquire the detection result by the detection unit and determine the type of recording medium on the basis of the detection result, and a second operation to apply a plurality of test voltages from the application unit to the transfer unit in order to adjust a transfer voltage and output an adjustment chart in which a plurality of test images are transferred to the recording medium; and an input unit for inputting an indication to the control unit. The control unit feeds a recording medium from the feeding unit toward the transfer unit and executes the first operation, and executes the second operation to transfer a plurality of test images to the recording medium from which the index has been detected by the detection unit in the first operation and output an adjustment chart, in accordance with one start indication inputted from the input unit.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus such as a copying machine, printer, facsimile machine, printing machine, or multifunction machine having a plurality of functions among them, which uses an electrophotographic or electrostatic recording method. [Background technology]

[0002] An image forming apparatus using an electrophotographic method or the like forms a toner image, which is a developed electrostatic latent image corresponding to input image data, on an image carrier such as a photosensitive drum, transfers the toner image onto a recording material, and then fixes the toner image on the recording material to perform printing. In addition, as a color image forming apparatus, an image forming apparatus using an intermediate transfer method as described below is known. An image forming apparatus using the intermediate transfer method forms a toner image on a first image carrier such as a plurality of photosensitive drums, transfers the toner image onto a second image carrier such as an intermediate transfer belt, and then transfers the toner image on the second image carrier onto the recording material. According to the intermediate transfer method, it becomes easy to form an image on various recording materials, so that the range of recording material selection can be expanded. The transfer of a toner image from an image carrier such as a photosensitive drum or an intermediate transfer belt to a transferee is often performed electrostatically by applying a transfer voltage to a transfer member that contacts the image carrier to form a transfer portion. Below, an image forming apparatus using an intermediate transfer method equipped with an intermediate transfer belt will be mainly described as an example.

[0003] In recent years, various types of recording materials (material, thickness, basis weight, surface properties, brand, etc.) are used to increase the added value of the finished product. The types of recording materials are classified according to the difference in surface smoothness (surface properties) such as fine paper and coated paper, and the difference in electrical resistance due to thickness and filler. The appropriate secondary transfer voltage for transferring a toner image to a recording material varies depending on the surface properties and electrical resistance of the recording material, and in order to obtain a good transferred image, it is necessary to set an appropriate secondary transfer voltage according to the recording material used. However, there are many types of recording materials in circulation. Therefore, even if the recording materials have the same basis weight and paper type category (plain paper, thick paper, thin paper, glossy paper, etc.), their electrical resistance may differ depending on the brand (manufacturer, product name, product number, etc.). Furthermore, the electrical resistance of a recording material changes significantly when it contains moisture from the surroundings, so even when the same recording material is used, it is necessary to set an appropriate secondary transfer voltage according to the environment (temperature, humidity) in which it is used. If the secondary transfer voltage is not appropriate for the type and condition of the recording material, image defects such as low image density (a phenomenon in which the toner image is not transferred sufficiently when the transfer voltage is too low) and blank areas (a phenomenon in which the toner image is not transferred partially when the transfer voltage is too high) are likely to occur.

[0004] Conventionally, in order to set an appropriate secondary transfer voltage according to the type and condition of the recording material, a mode provided in the image forming apparatus that allows the adjustment value of the image forming conditions to be changed, called a service mode or a user mode, is often used. In adjusting the secondary transfer voltage using this service mode or user mode, the user operates the image forming apparatus so as to output an image to be actually formed on the recording material to be actually used while changing the setting of the secondary transfer voltage. In this way, the user searches for an appropriate secondary transfer voltage. However, adjustment using this method often requires the task of outputting images on a relatively large number of recording materials while changing the setting of the secondary transfer voltage, which may impose a burden on the user.

[0005] In order to reduce the burden on the user as described above, an adjustment mode (simplified adjustment mode) using an adjustment chart such as the following is known (Patent Document 1). In this adjustment mode, the user operates the image forming apparatus so as to output a predetermined adjustment chart including a plurality of patches (test images) using a recording material that is actually used. The adjustment chart is output by transferring a plurality of patches to a recording material with a secondary transfer voltage switched for each patch. For example, a secondary transfer voltage in which an adjustment value ΔV that is changed by a predetermined change width with respect to a standard secondary transfer voltage is applied to a secondary transfer member, so that the plurality of patches are transferred to the recording material. The user visually checks the transferability of each patch transferred to the recording material with different secondary transfer voltages, and selects an adjustment value ΔV (i.e., secondary transfer voltage) corresponding to the patch with the optimal transferability. Then, the adjustment value ΔV is reflected in the transfer condition (secondary transfer voltage setting) during normal image formation. This makes it possible to obtain an appropriate transferability according to the type and state of the recording material. In addition, in some cases, the image forming apparatus is provided with a semi-automatic adjustment function that automatically selects an appropriate secondary transfer voltage based on density data acquired by reading the output adjustment chart with a reading device instead of visually checking the adjustment chart. The semi-automatic adjustment function automates the task of the user visually checking the adjustment chart, selecting and inputting an appropriate secondary transfer voltage, thereby reducing the burden on the user and shortening the work time.

[0006] Meanwhile, there is known an image forming apparatus equipped with an internal sensor that distinguishes the type of recording material (Patent Document 2). In this image forming apparatus, the type of recording material is automatically distinguished, and image forming conditions are set according to the distinguishing result. The sensors used include a sensor that uses light to detect the surface properties of the recording material, and a sensor that uses ultrasonic waves to detect the basis weight of the recording material. In addition, the image forming conditions set include transfer conditions (e.g., transfer voltage and conveying speed of the recording material during transfer) and fixing conditions (e.g., fixing temperature and conveying speed of the recording material during fixing). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2013-37185 A [Patent Document 2] JP 2009-029622 A Summary of the Invention [Problem to be solved by the invention]

[0008] In general, in an image forming apparatus, for example, a representative brand of recording material is selected in advance, and image forming conditions (transfer conditions, fixing conditions, etc.) are set for each type of recording material (for example, paper type category). A user operates the image forming apparatus to perform image formation by specifying the recording material to be used from among the types of recording material set in advance. However, as described above, there are a great many types of recording materials in circulation.

[0009] In view of this, some image forming apparatuses are provided with a recording material registration function so that, for example, a user can perform image formation under appropriate image forming conditions for a new recording material to be used by the user. With the recording material registration function, for example, the type of recording material to be newly set in the feeding section is selected and set from among the types of recording materials preset in the image forming apparatus.

[0010] However, it is possible that the user may not have sufficient information about the recording material, such as not having sufficient knowledge about the recording material. In this case, the user may select the wrong type of recording material in the recording material registration function. If the type of recording material selected by the user differs from the actual type of recording material, the transfer conditions and fixing conditions may not be appropriate, and image defects may occur.

[0011] In addition, for example, a recording material that a user wishes to register may have an electrical resistance different from the standard value, and therefore, it may be desirable to adjust (change) the secondary transfer voltage setting for that recording material from the standard setting that is preset in the image forming apparatus.

[0012] As described above, there is known an image forming apparatus that automatically determines the type of recording material using a sensor and sets image forming conditions according to the determination result. However, even if the type of recording material can be determined using a sensor, for example, the recording material may have characteristics (surface properties or electrical resistance) outside the specifications, or the electrical resistance of the recording material may differ from the standard value depending on the storage condition (moisture content) of the recording material. Therefore, even if the image forming apparatus has a function of setting image forming conditions according to the type of recording material determined using a sensor, it may be desired to adjust (change) the setting of the secondary transfer voltage from the standard setting previously set in the image forming apparatus according to the type of recording material.

[0013] It is conceivable that a user who does not have sufficient information about the recording material can use a function to automatically determine the type of recording material using a sensor provided in the image forming apparatus when adjusting the secondary transfer voltage. However, in this case, if the type of recording material is first determined using the sensor and then the secondary transfer voltage is adjusted in the adjustment mode for the determined type of recording material, this may impose a burden on the user. In addition, different recording materials are required for determining the type of recording material and for adjusting the secondary transfer voltage, which increases the amount of "waste paper" that is not used for image output.

[0014] SUMMARY OF THE PRESENT DISCLOSURE OF THE PRESENT DISCLOSURE It is therefore an object of the present invention to make it possible to easily adjust the transfer voltage while reducing the workload of the operator and reducing paper waste. [Means for solving the problem]

[0015] The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention includes an image carrier that carries a toner image, a transfer member forming a transfer section that transfers the toner image from the image carrier to a recording material, an application section that applies a voltage to the transfer section, a feeding section that feeds the recording material toward the transfer section, a detection section that detects an index that correlates with the type of the recording material from the recording material upstream of the transfer section in the transport direction of the recording material fed from the feeding section and transported to the transfer section, a first operation of acquiring a detection result by the detection section and determining the type of the recording material based on the detection result, and a second operation of adjusting a transfer voltage applied to the transfer section by the application section when the toner image is transferred to the recording material. and a control unit that controls a second operation in which the application unit applies multiple test voltages to the transfer unit to output an adjustment chart by transferring multiple test images onto a recording material, and an input unit that inputs instructions to the control unit, wherein the control unit is capable of controlling, in response to a single start instruction input from the input unit, to feed the recording material from the feeding unit toward the transfer unit to perform the first operation, and to transfer the multiple test images onto the recording material on which the index has been detected by the detection unit in the first operation, and to output the adjustment chart. Effect of the Invention

[0016] According to the present invention, it is possible to easily adjust the transfer voltage while reducing the workload of the operator and reducing paper waste. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Diagram 2] FIG. 2 is a block diagram showing a control configuration of the image forming apparatus. [Diagram 3] FIG. 2 is a block diagram showing a configuration of a recording material discrimination unit. [Figure 4] FIG. 4 is a flowchart illustrating a procedure for controlling a secondary transfer voltage. [Diagram 5] 6 is a graph showing an example of voltage-current characteristics obtained by controlling a secondary transfer voltage; [Figure 6] FIG. 4 is a schematic diagram showing an example of a table of recording material distribution voltages. [Figure 7] FIG. 4 is a schematic diagram of an adjustment chart. [Figure 8] FIG. 4 is a schematic diagram of an adjustment chart. [Figure 9] FIG. 11 is a flowchart showing the procedure of a recording material registration mode in the first embodiment. [Figure 10] FIG. 13 is a schematic diagram showing an example of a display screen relating to a recording material registration mode. [Figure 11] FIG. 13 is a schematic diagram showing an example of a display screen relating to a recording material registration mode. [Figure 12] FIG. 13 is a schematic diagram showing an example of a display screen relating to a recording material registration mode. [Figure 13] FIG. 11 is a graph showing an example of a result of reading the adjustment chart. [Figure 14] 10 is a graph illustrating the relationship between the electrical resistance of a recording material and a transfer current that flows when an adjustment chart is output. FIG. [Figure 15] FIG. 11 is a flowchart showing the procedure of a recording material registration mode in the first embodiment. [Figure 16] FIG. 13 is a schematic diagram showing an example of a display screen relating to a recording material registration mode. [Figure 17] FIG. 11 is a schematic cross-sectional view of another example of an image forming apparatus. [Figure 18] FIG. 13 is a schematic diagram showing an example of a display screen relating to an adjustment mode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

[0019] [Example 1] 1. Configuration and operation of image forming apparatus 1 is a schematic cross-sectional view of an image forming apparatus 1 according to this embodiment. The image forming apparatus 1 according to this embodiment is a tandem type multifunction machine that employs an intermediate transfer method and is capable of forming full-color images using an electrophotographic method (having the functions of a copier, printer, and facsimile machine).

[0020] As shown in FIG. 1, the image forming apparatus 1 includes an apparatus main body 10, a reading device 80, an automatic document feeder 81, an operation unit 70, and the like. The image forming apparatus 1 also includes a feed unit 90, an image forming unit 40, an ejection unit 48, a control unit 30, a temperature sensor 71, a humidity sensor 72, a recording material discrimination unit 300, and the like within the apparatus main body 10. The image forming apparatus 1 can form a full-color image on a recording material (sheet, transfer material, recording medium, media) according to image information (image signal) from the reading device 80 or an external device 200 (FIG. 2). Examples of the external device 200 include a host device such as a personal computer, a digital camera, and a smartphone. The recording material S is a material on which a toner image is formed, and specific examples include plain paper, a synthetic resin sheet that is a substitute for plain paper, cardboard, and an overhead projector sheet (OHT sheet). Here, the recording material S may be referred to as "paper", but even in this case, the recording material S includes a material other than paper or a material containing a material other than paper.

[0021] The image forming section 40 can form an image on the recording material S fed from the feeding section (feeding device) 90 based on image information. The image forming section 40 has image forming units 50y, 50m, 50C, 50k, toner bottles 41y, 41m, 41C, 41k, exposure devices 42y, 42m, 42C, 42k, an intermediate transfer unit 44, a secondary transfer device 45, and a fixing device 46. The four image forming units 50y, 50m, 50C, 50k form images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. Note that elements having the same or corresponding functions or configurations provided for each color may be generally described by omitting the suffixes y, m, c, and k of the reference numerals indicating that the elements are for any of the colors. The image forming apparatus 1 can form a monochrome image, such as a black monochrome image, or a multi-color image, using a single or several image forming units 50 as desired.

[0022] The image forming unit 50 has the following means. First, it has a photosensitive drum 51 which is a drum-type (cylindrical) photosensitive body (electrophotographic photosensitive body) as a first image carrier. It also has a charging roller 52 which is a roller-type charging member as a charging means. It also has a developing device 20 as a developing means. It also has a pre-exposure device 54 as a discharging means. It also has a drum cleaning device 55 as a photosensitive body cleaning means. The image forming unit 50 forms a toner image on an intermediate transfer belt 44b which will be described later. Also, the image forming unit 50 is integrated as a process cartridge and is detachably attached to the apparatus main body 10.

[0023] The photosensitive drum 51 is movable (rotatable) while carrying an electrostatic image (electrostatic latent image) or a toner image. In this embodiment, the photosensitive drum 51 is a negatively charged organic photoconductor (OPC) having an outer diameter of 30 mm. The photosensitive drum 51 has an aluminum cylinder as a base and a surface layer formed on the surface of the aluminum cylinder. In this embodiment, the surface layer has three layers, an undercoat layer, a photocharge generation layer, and a charge transport layer, which are applied and laminated on the base in the following order. When an image forming operation is started, the photosensitive drum 51 is rotated in the direction of the arrow in the figure (counterclockwise direction) at a predetermined process speed (circumferential speed), for example, 210 mm / sec, by a motor (not shown) as a driving means.

[0024] 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 made of a rubber roller that comes into contact with the surface of the photosensitive drum 51 and rotates in accordance with the rotation of the photosensitive drum 51. A charging power source 73 (FIG. 2) serving as a charging voltage application means (charging voltage application section) is connected to the charging roller 52. The charging power source 73 applies a predetermined charging voltage (charging bias), which is a DC voltage of negative polarity (same polarity as the charging polarity of the photosensitive drum 51), to the charging roller 52 during charging.

[0025] The charged surface of the photosensitive drum 51 is scanned and exposed by the exposure device 42 based on image information, and an electrostatic image is formed on the photosensitive drum 51. In this embodiment, the exposure device 42 is configured as a laser scanner. The exposure device 42 emits laser light in accordance with image information of separated colors output from the control unit 30, and scans and exposes the surface (outer circumferential surface) of the photosensitive drum 51.

[0026] The electrostatic image formed on the photosensitive drum 51 is developed (visualized) by supplying toner by the developing device 20, and a toner image is formed on the photosensitive drum 51. In this embodiment, the developing device 20 contains a two-component developer including non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as a developer. Toner is supplied to the developing device 20 from a toner bottle 41. The developing device 20 has a developing sleeve 24 as a developer carrier. The developing sleeve 24 is made of a non-magnetic material (aluminum in this embodiment) such as aluminum or non-magnetic stainless steel. Inside the developing sleeve 24, a roller-shaped magnet roller is fixed and arranged so as not to rotate relative to the main body (developing container) of the developing device 20. The developing sleeve 24 carries the developer and transports it to a developing area facing the photosensitive drum 51. A developing power source 74 (FIG. 2) as a developing voltage application means (developing voltage application unit) is connected to the developing sleeve 24. During development, the development power supply 74 applies a predetermined development voltage (development bias) containing a DC component of negative polarity (same polarity as the charging polarity of the photosensitive drum 51) to the development sleeve 24. 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, which has been uniformly charged and then exposed to light, thereby reducing the absolute value of the potential (reverse development method). In this embodiment, the normal charging polarity of the toner, which is the main charging polarity of the toner during development, is negative polarity.

[0027] The intermediate transfer unit 44 is disposed so as to face the four photosensitive drums 51y, 51m, 51c, and 51k. The intermediate transfer unit 44 has an intermediate transfer belt 44b, which is an intermediate transfer body formed of an endless belt as a second image carrier. The intermediate transfer belt 44b is wound around a driving roller 44a, a tension roller 44d, and a secondary transfer inner roller 45a as a plurality of tension rollers (support rollers), and is stretched with a predetermined tension. The intermediate transfer belt 44b is movable (rotatable) while carrying a toner image. The driving roller 44a is rotated by a motor (not shown) as a driving means. The tension roller 44d is biased in a direction to push the intermediate transfer belt 44b from the inner peripheral surface side to the outer peripheral surface side by a tension spring (not shown) as a biasing member as a biasing means. As a result, a tension of about 29 to 118 N (about 3 to 12 kgf) is applied to the intermediate transfer belt 44b. The secondary transfer inner roller 45a constitutes the secondary transfer device 45 as described later. The intermediate transfer belt 44b receives a driving force as the driving roller 44a is driven to rotate, and rotates (circulates) 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. In addition, primary transfer rollers 47y, 47m, 47c, and 47k, which are roller-type primary transfer members as primary transfer means, are arranged on the inner peripheral surface side of the intermediate transfer belt 44b in correspondence with the photosensitive drums 51y, 51m, 51C, and 51k. The primary transfer roller 47 is pressed toward the photosensitive drum 51 and abuts against the photosensitive drum 51 via the intermediate transfer belt 44b, forming a primary transfer portion (primary transfer nip) N1 where the photosensitive drum 51 and the intermediate transfer belt 44b abut against each other. The tension rollers other than the driving roller 44a and each primary transfer roller 47 are driven to rotate in accordance with the rotation of the intermediate transfer belt 44b. The intermediate transfer unit 44 includes an intermediate transfer belt 44b, a tension roller for the intermediate transfer belt 44b, primary transfer rollers 47, a belt cleaning device 49 (described later), and the like.

[0028] The toner image formed on the photosensitive drum 51 is transferred (primary transfer) onto the rotating intermediate transfer belt 44b as a transfer target at the primary transfer section N1. A primary transfer power supply 75 (FIG. 2) is connected to the primary transfer roller 47 as a primary transfer voltage application means (primary transfer voltage application section). The primary transfer power supply 75 applies a primary transfer voltage (primary transfer bias) to the primary transfer roller 47 during primary transfer, which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner. This forms a primary transfer contrast, which is a potential difference between the surface potential of the photosensitive drum 51 and the potential of the primary transfer roller 47, and the negative polarity toner image on the photosensitive drum 51 is electrostatically attracted onto the intermediate transfer belt 44b and transferred onto the intermediate transfer belt 44b. For example, when a full-color image is formed, the toner images of yellow, magenta, cyan, and black formed on the photosensitive drums 51y, 51m, 51c, and 51k are sequentially primary transferred so as to be superimposed on the intermediate transfer belt 44b. A voltage detection sensor (voltage detection circuit) 75a as a voltage detection means for detecting an output voltage, and a current detection sensor (current detection circuit) 75b as a current detection means for detecting an output current are connected to the primary transfer power supply 75 (FIG. 2). In this embodiment, primary transfer power supplies 75y, 75m, 75c, and 75k are provided for primary transfer rollers 47y, 47m, 47c, and 47k, respectively, and the primary transfer voltages applied to primary transfer rollers 47y, 47m, 47c, and 47k can be individually controlled.

[0029] Here, in this embodiment, the primary transfer roller 47 is configured as a metal roller formed of metal such as SUM (sulfur and sulfur composite free-cutting steel) or SUS (stainless steel). Also, in this embodiment, the primary transfer roller 47 has a straight shape in which the outer diameter of the roller part that contacts the intermediate transfer belt 44b is substantially uniform over the entire area in the rotation axis direction, and the outer diameter of the roller part is about 6 to 10 mm.

[0030] In this embodiment, the intermediate transfer belt 44b is an endless belt made of a single layer. Examples of materials constituting the intermediate transfer belt 44b include polyimide, polycarbonate, polyvinylidene fluoride (PVDF), polyphenylene sulfide, polyethylene, polypropylene, polystyrene, polyamide, polysulfone, and polyarylate. Resins such as polyethylene terephthalate, polybutylene terephthalate, polyethersulfone, polyethernitrile, ethylene tetrafluoroethylene copolymer, and polyether ether ketone, or mixtures of these resins, can be used. In this embodiment, polyimide resin or polyether ether ketone resin is used as the material constituting the intermediate transfer belt 44b. In this embodiment, the thickness of the intermediate transfer belt 44b is about 60 to 70 μm. In this embodiment, the surface resistivity of the intermediate transfer belt 44b is 1.0×10 9 Ω / □ or more, 2.0×10 11 In this embodiment, the volume resistivity of the intermediate transfer belt 44b is 4.0×10 9 Ω cm or more, 6.0×10 11 The electrical resistance of the intermediate transfer belt 44b was measured using a Hiresta UP (manufactured by Mitsubishi Chemical) as a measuring device and a URS (guard electrode outer diameter φ17.9 mm) (manufactured by Mitsubishi Chemical) as a measuring probe under the measurement conditions of an applied voltage of 100 V and a charge time of 10 seconds.

[0031] On the outer peripheral surface side of the intermediate transfer belt 44b, a secondary transfer outer roller 45b, which is a roller-type secondary transfer member as a secondary transfer means and which constitutes the secondary transfer device 45 together with the secondary transfer inner roller 45a, is arranged. The secondary transfer outer roller 45b is pressed toward the secondary transfer inner roller 45a and abuts against the secondary transfer inner roller 45a via the intermediate transfer belt 44b to form a secondary transfer portion (secondary transfer nip) N2 where the intermediate transfer belt 44b and the secondary transfer outer roller 45b abut. The toner image formed on the intermediate transfer belt 44b is transferred (secondary transfer) onto the recording material S as a transfer target that is sandwiched and conveyed 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 secondary transfer. That is, in this embodiment, the secondary transfer device 45 is configured to have the secondary transfer inner roller 45a as an opposing member and the secondary transfer outer roller 45b as a secondary transfer member. A secondary transfer power supply 76 (FIG. 2) is connected to the outer secondary transfer roller 45b as a secondary transfer voltage application means (secondary transfer voltage application section). The secondary transfer power supply 76 applies a secondary transfer voltage (secondary transfer bias) which is a DC voltage of a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) to the outer secondary transfer roller 45b during secondary transfer. A voltage detection sensor (voltage detection circuit) 76a as a voltage detection means for detecting an output voltage and a current detection sensor (current detection circuit) 76b as a current detection means for detecting an output current are connected to the secondary transfer power supply 76 (FIG. 2). The current detection sensor 76b can detect the current flowing through the outer secondary transfer roller 45b. In this embodiment, the core metal of the inner secondary transfer roller 45a is connected to a ground potential (electrically grounded). When the recording material S is supplied to the secondary transfer section N2, a constant voltage controlled secondary transfer voltage of a polarity opposite to the normal charging polarity of the toner is applied to the outer secondary transfer roller 45b. In this embodiment, for example, a secondary transfer voltage of 1 to 7 kV is applied, and a current of 40 to 120 μA is caused to flow, so that the toner image on the intermediate transfer belt 44b is secondarily transferred onto the recording material S.Alternatively, the secondary transfer power supply 76 may apply a secondary transfer voltage having the same polarity as the normal charging polarity of the toner to the secondary transfer inner roller 45a as the secondary transfer member, and the secondary transfer outer roller 45b as the opposing member may be electrically grounded.

[0032] In this embodiment, the inner secondary transfer roller 45a is configured to have a core metal and an elastic layer made of EPDM (ethylene propylene diene rubber) provided around the core metal. In this embodiment, the inner secondary transfer roller 45a is formed so that the outer diameter of the roller part that contacts the intermediate transfer belt 44b is 20 mm, the thickness of the elastic layer is 0.5 mm, and the hardness is set to, for example, 70° (Asker C).

[0033] In this embodiment, the secondary transfer outer roller 45b is configured to have a core metal and an elastic layer formed of NBR (nitrile rubber) or EPDM containing an ion conductive agent such as a metal complex provided around the core metal. In this embodiment, the secondary transfer outer roller 45b is formed so that the outer diameter of the core metal is 12 mm, and the outer diameter of the roller portion that contacts the intermediate transfer belt 44b is 24 mm. In this embodiment, the resistance value of the secondary transfer outer roller 45b is 3.0×10 7 ~5.0×10 7 In the secondary transfer portion N2, the resistance values ​​of the inner secondary transfer roller 45a and the intermediate transfer belt 44b are sufficiently smaller than the resistance value of the outer secondary transfer roller 45b.

[0034] The recording material S is fed from the feeding section 90 in parallel with the above-mentioned toner image forming operation. That is, the recording material S is stacked and stored in a recording material cassette 91 serving as a recording material storage section. The recording material S stored in the recording material cassette 91 is sent to a conveying path 93 by a feeding roller 92 serving as a feeding member. The recording material S sent to the conveying path 93 is conveyed to a registration roller pair 43 serving as a conveying member by a conveying roller pair 94 serving as a conveying member. The recording material S is corrected for skew by the registration roller pair 43, and is supplied to the secondary transfer section N2 in a timing match with the toner image on the intermediate transfer belt 44b. The recording material cassette 91, the feeding roller 92, the conveying path 93, the conveying roller pair 94, and the like constitute the feeding section 90. Note that the feeding section 90 may be provided with a plurality of recording material cassettes 91. In addition to the recording material cassette 91, the feeding section 90 may be provided with a manual feed tray on which the recording material S is placed.

[0035] The recording material S onto which the toner image has been transferred is transported to a fixing device 46 as a fixing means. The fixing device 46 has a fixing roller 46a incorporating a heater as a heating means, and a pressure roller 46b that is in pressure contact with the fixing roller 46a. The fixing device 46 heats and presses the recording material S carrying the unfixed toner image by sandwiching it between the fixing roller 46a and the pressure roller 46b and transporting it, thereby fixing (melting and bonding) the toner image onto the recording material S. The temperature (fixing temperature) of the fixing roller 46a is detected by a fixing temperature sensor 77 (FIG. 2).

[0036] The recording material S on which the toner image has been fixed is conveyed through a discharge path 48a by a pair of discharge rollers 48b as a conveying member, and is discharged (output) from a discharge port 48c and stacked on a discharge tray 48d provided outside the apparatus main body 10. A discharge section (discharge device) 48 is configured by the discharge path 48a, the pair of discharge rollers 48b, the discharge port 48c, the discharge tray 48d, and the like. In this embodiment, the image forming apparatus 1 is capable of double-sided image formation (double-sided printing, automatic double-sided printing) in which images are formed on both sides of the recording material S. Between the fixing device 46 and the discharge port 48c, a reversing conveying path 12 is provided for turning over the recording material S after the toner image has been fixed on the first side and supplying it again to the secondary transfer section N2. During double-sided image formation, the recording material S after the toner image has been fixed on the first side is guided to the reversing conveying path 12. The recording material S has its conveying direction reversed by a switchback roller pair 13 provided in the reversing conveying path 12, and is guided to a double-sided conveying path 14. The recording material S is then sent to a conveying path 93 by a re-conveying roller pair 15 provided in the double-sided conveying path 14, conveyed to a registration roller pair 43, and supplied to a secondary transfer section N2 by the registration roller pair 43. Thereafter, a toner image is secondarily transferred to the second side of the recording material S in the same manner as in the image formation on the first side, and after the toner image is fixed, the recording material S is discharged to an output tray 48d. The reversing conveying path 12, the switchback roller pair 13, the double-sided conveying path 14, the re-conveying roller pair 15, etc. form a double-sided conveying section (double-sided conveying device) 11.

[0037] After the primary transfer, the surface of the photosensitive drum 51 is neutralized by the pre-exposure device 54. In addition, deposits such as toner (primary transfer residual toner) remaining on the photosensitive drum 51 without being transferred to the intermediate transfer belt 44b during the primary transfer are removed from the photosensitive drum 51 and collected by the drum cleaning device 55. The drum cleaning device 55 scrapes off deposits from the surface of the rotating photosensitive drum 51 using a cleaning blade as a cleaning member that contacts the surface of the photosensitive drum 51 and stores the scraped off deposits in a cleaning container. The cleaning blade is contacted with the surface of the photosensitive drum 51 such that the tip of the free end side faces the upstream side of the rotation direction of the photosensitive drum 51, that is, in the counter direction to the rotation direction of the photosensitive drum 51. In this embodiment, the cleaning blade is an elastic blade made of a material mainly composed of urethane rubber with a free length of 8 mm, and is contacted with the surface of the photosensitive drum 51 with a predetermined pressing force. In addition, any adhering matter such as toner (secondary transfer residual toner) that remains on the intermediate transfer belt 44b without being transferred to the recording material S during the secondary transfer is removed and collected from the intermediate transfer belt 44b by a belt cleaning device 49, which serves as an intermediate transfer body cleaning means.

[0038] Further, on the upper part of the device main body 10, a reading device (reading section) 80 as a reading means and an automatic document feeder (document feeder) 81 as a document feeder are arranged. The reading device 80 has a platen glass 82, a light source 83, an optical system 84 including a group of mirrors 84a and an imaging lens 84b, and a reading element 85 such as a CCD. The reading device 80 reads an image on a document such as paper. The automatic document feeder 81 automatically conveys a document such as paper on which an image is formed to the reading device 80. In this embodiment, the reading device 80 can sequentially read an image of a document (recording material S on which an image is formed) arranged on the platen glass 82 by the reading element 85 via the optical system 84 while scanning and exposing the image by the movable light source 82. In this case, the reading device 80 sequentially illuminates the document arranged on the platen glass 82 by the moving light source 83, and sequentially forms an image of reflected light from the document on the reading element 85 via the optical system 84. This allows the reading element 85 to read the image of the document at a predetermined dot density. Also, in this embodiment, the reading device 80 sequentially exposes the image of the document transported by the automatic document feeder 81 to light from the light source 82 as the document is transported, and sequentially reads the image by the reading element 85 via the optical system 84. In this case, the reading device 80 sequentially illuminates the document passing a predetermined reading position on the platen glass 82 with the light source 83, and sequentially forms an image of the light reflected from the document on the reading element 85 via the optical system 84. This allows the reading element 85 to read the image of the document at a predetermined dot density.

[0039] In this way, the reading device 80 optically reads an image on the recording material S placed on the platen glass 82 or conveyed by the automatic document conveying device 81, and converts it into an electric signal. For example, when the image forming apparatus 1 operates as a copier, the image of the document read by the reading device 80 is sent to the image processing unit of the control unit 30 as image data of three colors, for example, red (R), green (G), and blue (B) (each 8 bits). In the image processing unit, the image data of the document is subjected to a predetermined image processing as necessary, and is converted into image data of four colors, yellow, magenta, cyan, and black. The image processing includes shading correction, positional deviation correction, brightness / color space conversion, gamma correction, frame erasure, color / movement editing, and the like. The image data corresponding to the four colors, yellow, magenta, cyan, and black, are sequentially sent to the exposure devices 42y, 42m, 42c, and 42k, respectively, and the above-mentioned image exposure is performed according to this image data. As will be described in detail later, the reading device 80 is also used in the adjustment mode (or the recording material registration mode) to read patches of the adjustment chart, that is, to obtain density information (brightness information).

[0040] Further, a recording material discrimination unit 300 is provided downstream of the pair of registration rollers 43 and upstream of the secondary transfer portion N2 in the conveying direction of the recording material S as a recording material information acquisition means (recording material information acquisition portion) that acquires information about the recording material S. The recording material discrimination unit 300 will be described in detail later.

[0041] 2. Control configuration FIG. 2 is a block diagram showing the control configuration of the image forming apparatus 1 of this embodiment. The image forming apparatus 1 is provided with a control unit (control circuit) 30 as a control means. The control unit 30 is configured with a computer. The control unit 30 is configured to have, for example, a CPU 31 as an arithmetic processing unit (arithmetic processing section), a ROM 32 and a RAM 33 as storage means (storage section), an input / output circuit (I / F) 34 that inputs and outputs signals between the control unit 30 and an external device, and the like. The CPU 31 is a microprocessor that controls the entire control of the image forming apparatus 1, and is the main body of the system controller. The ROM (including a rewritable one) 32 stores programs that control each section of the image forming apparatus 1, various setting values, and the like. The RAM 33 temporarily stores data related to control, and the like.

[0042] The CPU 31 is connected to the feeding section 90, the image forming section 40, the discharge section 48, and the operation section 70 via the input / output circuit 34, and exchanges signals with each of these sections and controls the operation of each of these sections. The ROM 32 stores an image formation control sequence for forming an image on the recording material S. For example, the control section 30 is connected to a charging power supply 73, a developing power supply 74, a primary transfer power supply 75, a secondary transfer power supply 76, and the like, which are each controlled by a signal from the control section 30. Although not shown in the figure, the charging power supply 73 and the developing power supply 74 may be provided independently for each image forming unit 50. The control section 30 is also connected to a temperature sensor 71, a humidity sensor 72, a voltage detection sensor 75a and a current detection sensor 75b of the primary transfer power supply 75, a voltage detection sensor 76a and a current detection sensor 76b of the secondary transfer power supply 76, a fixing temperature sensor 77, a recording material discrimination unit 300, and the like. In this embodiment, the temperature sensor 71 can detect the temperature (internal temperature) inside the device body 10 of the image forming apparatus 1. Also, in this embodiment, the humidity sensor 72 can detect the humidity (internal humidity) inside the device body 10 of the image forming apparatus 1. The environment may be at least one of the temperature and humidity inside or outside the image forming apparatus 1. Signals (information) indicating the detection results of each sensor are input to the control unit 30.

[0043] The operation unit 70 has operation buttons (keys) as input means and a display unit 70a configured with a liquid crystal panel (display) as display means. In this embodiment, the display unit 70a is configured as a touch panel and also functions as an input means. An operator such as a user or a service person (herein, simply referred to as a "user") can cause the image forming apparatus 1 to execute a job by operating the operation unit 70 as an input unit. The control unit 30 receives a signal from the operation unit 70 and operates various devices of the image forming apparatus 1. The image forming apparatus 1 can also execute a job based on an image formation signal (image data, control command) from an external device 200 such as a personal computer.

[0044] In this embodiment, the control unit 30 has functions as an image forming process unit, an ATVC control process unit, a recording material registration unit, a primary transfer voltage storage unit / calculation unit, a secondary transfer voltage storage unit / calculation unit, and the like. In this embodiment, these respective process units and storage units / calculation units are realized by the CPU 31 and the RAM 33 that operate according to the programs and data stored in the ROM 32. For example, the control unit 30 can execute a job as an image forming process unit. Also, the control unit 30 can execute ATVC control of the primary transfer unit and the secondary transfer unit as an ATVC control process unit. The ATVC control will be described in detail later. Also, the control unit 30 can execute control related to the registration of the recording material S as a recording material registration unit. The registration of the recording material S will be described in detail later. Also, the control unit 30 can execute control related to the setting (adjustment) and storage of the primary transfer voltage and the secondary transfer voltage as a primary transfer voltage storage unit / calculation unit and a secondary transfer voltage storage unit / calculation unit. An adjustment mode (or a recording material registration mode) for setting (adjusting) the secondary transfer voltage will be described in detail later. The control unit 30 can switch between a multiple color mode in which a primary transfer voltage is applied to multiple primary transfer rollers 47 to form an image in multiple colors, and a monochrome mode in which a primary transfer voltage is applied to only one of the multiple primary transfer rollers 47 to form an image in a single color.

[0045] Here, a job (print job) is a series of operations that is started by a single start instruction and forms and outputs an image on one or more recording materials S. A job generally includes an image forming process, a pre-rotation process (preparatory operation), a paper spacing process when forming images on multiple recording materials S, and a post-rotation process (organizing operation).

[0046] The types of recording material S include classifications of recording material S according to information about any recording material S, such as attributes (so-called paper type categories) based on general characteristics (basis weight, thickness, surface properties, light reflectivity, light transmittance, etc.) such as plain paper, high-quality paper, gloss paper (glossy paper), coated paper, embossed paper, thick paper, thin paper, rough paper, etc., numerical values ​​or numerical ranges of basis weight, thickness, stiffness, etc., brand (including manufacturer, product name, product number, etc.), or combinations thereof. In other words, each recording material S classified according to information about the recording material S can be considered to constitute a type of recording material S. For example, the following types (e.g. paper type categories) are set as types of recording material S in the image forming apparatus 1, and image formation conditions (transfer conditions, fixing conditions, etc.) corresponding to each type are set. (1) Thin paper (basis weight: up to 64 g / m 2 ) (2) Plain paper (basis weight: 65~105g / m 2 ) (3) Cardboard 1 (basis weight: 106-135g / m 2 ) (4) Cardboard 2 (grammage: 136 g / m 2 ~) (5) Glossy paper (6) Gloss film (7) OHT Sheet (Overhead Transparency Sheet)

[0047] The types of the recording material S can be determined by the recording material determination unit 300 based on the basis weight and surface properties of the recording material S. For example, based on the amount of light reflected from the recording material S (corresponding to light transmittance), it can be determined whether the recording material S is the above-mentioned (7). Also, based on the surface smoothness of the recording material S (the ratio of shadows in an image obtained based on the amount of light reflected from the recording material S), it can be determined whether the recording material S is the above-mentioned (1) to (4), (5), or (6). Also, based on the basis weight of the recording material S (the peak value of the waveform of ultrasonic waves transmitted through the recording material S), it can be determined whether the recording material is one of the above-mentioned (1) to (4). Note that thin paper and plain paper may be classified into a plurality of paper type categories, such as thin paper 1, thin paper 2, plain paper 1, plain paper 2, etc., according to the basis weight classification. Also, thick paper may be classified into more paper type categories according to the basis weight classification, or may be classified into one paper type category. It should be noted that the types of recording material S that can be set in the image forming apparatus 1 are not limited to those mentioned above. Instead of any of the above types of recording material S, or in addition to the above types of recording material S, coated paper, rough paper, etc. can be set. In addition, the configuration of the recording material discrimination means (media sensor) that discriminates the type of recording material S and the method of discriminating the type of recording material S using the same can be any available one, such as a known one.

[0048] 3. Recording material discrimination unit Next, the recording material discrimination unit 300 in this embodiment will be described. Fig. 2 is a block diagram for explaining the configuration of the recording material discrimination unit 300. The recording material discrimination unit 300, which serves as a recording material information acquisition means (recording material information acquisition section) for acquiring information about the recording material S, is configured to include a basis weight detection section 301 that detects the basis weight of the recording material S, and a surface property detection section 311 that detects the surface property of the recording material S. The basis weight detection section 301 acquires information about the basis weight as a first property of the recording material S, as information about the recording material S. The surface property detection section 311 acquires information about the surface smoothness (surface property) as a second property of the recording material S, as information about the recording material S.

[0049] The basis weight detection unit 301 has an ultrasonic transmission unit 303 that transmits ultrasonic waves, and an ultrasonic reception unit 304 that receives the ultrasonic waves transmitted from the ultrasonic transmission unit 303. The basis weight detection unit 301 also has an ultrasonic control unit 302. Here, the ultrasonic transmission unit 303 and the ultrasonic reception unit 304 are arranged facing each other so as to sandwich the conveyed recording material S. The ultrasonic transmission unit 303 and the ultrasonic reception unit 304 are each connected to the ultrasonic control unit 302. The ultrasonic transmission unit 303 transmits ultrasonic waves of a predetermined frequency according to an instruction from the ultrasonic control unit 302. The ultrasonic reception unit 304 receives the ultrasonic waves that have passed through the recording material S, and outputs a voltage value according to the received ultrasonic waves. The ultrasonic control unit 302 outputs the peak value of the voltage value output from the reception unit 304 to the control unit 30.

[0050] The peak value of the waveform of the ultrasonic waves transmitted through the recording material S attenuates according to the basis weight of the recording material S. For example, the peak value of the ultrasonic waves is large for a recording material S with a small basis weight, and is small for a recording material S with a large basis weight. In this way, the basis weight detection unit 301 irradiates the recording material S with ultrasonic waves and detects the ultrasonic waves transmitted through the recording material S as an index correlating with the type of recording material S. The control unit 30 determines the basis weight of the recording material S based on the peak value output from the ultrasonic control unit 302. Then, for example, if the control unit 30 determines that the basis weight is small, it determines that the paper type category of the recording material S is thin paper, and if the control unit 30 determines that the basis weight is large, it determines that the paper type category of the recording material S is thick paper.

[0051] The following effects can be obtained by appropriately setting the fixing temperature of the fixing device 46 according to the basis weight or paper type category of the recording material S determined by the control unit 30. For example, in the case of a recording material S having a small basis weight such as thin paper, the required power is reduced by setting the fixing temperature low. Conversely, in the case of a recording material S having a large basis weight such as thick paper, the fixing property is improved by setting the fixing temperature high or slowing down the conveying speed of the recording material S. Also, in the case of a recording material S having a small basis weight such as thin paper, the secondary transfer voltage is set low to suppress the occurrence of image defects such as white spots due to the transfer voltage being too high. Conversely, in the case of a recording material S having a large basis weight such as thick paper, the secondary transfer voltage is set high to suppress the occurrence of image defects such as low density. In this way, the control unit 30 controls the image forming conditions (transfer conditions, fixing conditions, etc.) based on the determination result of the basis weight or paper type category of the recording material S. Note that the control unit 30 may directly control the image forming conditions based on the peak value output from the ultrasonic control unit 302 without determining the basis weight or paper type category of the recording material S.

[0052] The surface property detection unit 311 includes a light source 314, which is an irradiation unit that irradiates light onto the surface of the recording material S, and a light receiving element (imaging unit) 316 that receives light reflected from the surface of the recording material S and captures the received light as an image. In this embodiment, a line sensor in which multiple light receiving elements are arranged in the width direction (direction substantially perpendicular to the conveying direction) of the recording material S is used as the light receiving element 316. By using the line sensor, it is possible to capture an image while conveying the recording material S. In addition, the surface property detection unit 311 includes a light source driving circuit 313, a waveform shaping circuit 315, and a surface property detection processing unit 312. The light source driving circuit 313 controls the amount of light emitted by the light source 314, the light emission period, etc. The waveform shaping circuit 315 converts the intensity of light received by the multiple light receiving elements of the imaging unit 316 into a voltage value and outputs it as image information. The surface property detection processing unit 312 transmits and receives signals between the light source circuit 313 and the waveform shaping circuit 315. For example, the surface property detection processor 312 issues an instruction to start a detection operation to the light source circuit 313. Furthermore, based on the image information output from the waveform shaping circuit 315, the surface property detection processor 312 outputs information related to the surface property, such as the difference (Dmax-Dmin) between the maximum density value (Dmax) and the minimum density value (Dmin) included in the image information, to the control unit 30.

[0053] The captured image changes depending on the difference in the surface properties (unevenness) of the recording material S. For example, in the case of a recording material S with a rough surface (deep unevenness), the irradiated light creates an image with a large proportion of shadows (large Dmax-Dmin value). On the other hand, in the case of a recording material S with a relatively smooth surface (shallow unevenness), the image has few shadows (small Dmax-Dmin value). In this way, the surface property detection unit 311 irradiates the recording material S with light and detects the light passing through the recording material S as an index correlating with the type of the recording material S. The control unit 30 determines the surface properties of the recording material S based on the information on the surface properties of the recording material S (such as the Dmax-Dmin value) output from the surface property detection processing unit 312. Then, for example, when the control unit 30 determines that the surface of the recording material S is rough, it determines that the paper type category of the recording material S is rough paper, and when the control unit 30 determines that the surface of the recording material S is smooth, it determines that the paper type category of the recording material S is coated paper.

[0054] A recording material S with a smooth surface such as coated paper has a relatively high electrical resistance, and may require a large transfer current or a high transfer voltage to transfer the toner compared to a recording material S with a rough surface such as rough paper. Also, a recording material S with a rough surface such as rough paper may require a higher fixing temperature to sufficiently fix the toner. Therefore, it is also effective for improving the image quality if the control unit 30 controls the transfer conditions (transfer current and transfer voltage) and fixing conditions according to the determination result of the surface property or paper type category of the recording material S. In this way, the control unit 30 controls the image formation conditions (transfer conditions, fixing conditions, etc.) based on the determination result of the surface property or paper type category of the recording material S. Note that the control unit 30 may directly control the image formation conditions based on the information output from the waveform shaping circuit 315 without determining the surface property or paper type category of the recording material S.

[0055] The recording material discrimination unit 300 may detect only either the basis weight or the surface property of the recording material S. For example, the recording material discrimination unit 300 may have only either the basis weight detection unit 301 or the surface property detection unit 311 similar to the above. Detecting both the basis weight and the surface property of the recording material S as in this embodiment is preferable because it broadens the range of types of recording material S that can be discriminated, but it is possible to discriminate the appropriate type of recording material S depending on the characteristics of the recording material S that can be detected.

[0056] 4. Secondary transfer voltage control Next, the control of the secondary transfer voltage will be described. FIG. 4 is a flow chart showing an outline of the procedure for controlling the secondary transfer voltage in this embodiment. Generally, there are constant voltage control and constant current control for controlling the secondary transfer voltage, but this embodiment uses constant voltage control. Note that constant voltage control is a control that adjusts the output of a power source so that the voltage applied to the target is approximately constant at a target voltage. Also, constant current control is a control that adjusts the output of a power source so that the current supplied to the target is approximately constant at a target current.

[0057] First, when the control unit 30 acquires job information from the operation unit 70 or the external device 200, it starts the job operation (S1). The job information includes information on the type of recording material S specified by the user (e.g., paper type category) and information on the size (width, length) of the recording material S. Furthermore, when a job is started from the external device 200, the job information includes image information. Furthermore, when a job is started from the operation unit 70, the control unit 30 acquires image information from the reading device 80 or the like. The control unit 30 writes the image information and job information to the RAM 33 (S2).

[0058] Next, the control unit 30 acquires environmental information detected by the temperature sensor 71 and the humidity sensor 72 (S3). In addition, the ROM 32 stores information indicating the correlation between the environmental information and the target transfer current Itarget for transferring the toner image on the intermediate transfer belt 44b onto the recording material S. The control unit 30 obtains the target transfer current Itarget corresponding to the environment from the data indicating the relationship between the environmental information and the target transfer current Itarget based on the environmental information read in S3. Then, the control unit 30 writes this target current Itarget into the RAM 33 (S4). The reason why the target transfer current Itarget is changed according to the environmental information is because the charge amount of the toner changes depending on the environment. The data indicating the relationship between the environmental information and the target transfer current Itarget is obtained in advance by an experiment or the like.

[0059] Next, the control unit 30 acquires information on the electrical resistance of the secondary transfer unit N2 before the toner image on the intermediate transfer belt 44b and the recording material S to which the toner image is transferred arrive at the secondary transfer unit N2 (S5). That is, in a state in which the secondary transfer outer roller 45b and the intermediate transfer belt 44b are in contact with each other, a predetermined voltage of multiple levels is supplied from the secondary transfer power source 76 to the secondary transfer outer roller 45b. Then, the current detection sensor 76b detects the current when the predetermined voltage is being supplied, and acquires the relationship between the voltage and the current (voltage-current characteristic) as shown in FIG. 5. The control unit 30 writes the information on this voltage-current characteristic to the RAM 33. This voltage-current characteristic changes according to the electrical resistance of the secondary transfer unit N2. In the configuration of this embodiment, this voltage-current characteristic does not change linearly (proportional) to the voltage, but changes so that the current changes in such a way that it is expressed by a polynomial of the voltage that is quadratic or higher (quadratic in this embodiment). Therefore, in this embodiment, the predetermined voltage or current supplied when obtaining information about the electrical resistance of the secondary transfer portion N2 is multi-staged at three or more points so that the voltage-current characteristic can be expressed by a polynomial.

[0060] Next, the control unit 30 determines the voltage to be applied from the secondary transfer power source 76 to the secondary transfer outer roller 45b (S6). That is, the control unit 30 determines a base voltage Vb, which is a voltage required to flow the target transfer current Itarget in a state where the recording material S is not present in the secondary transfer portion N2, based on the target transfer current Itarget written in the RAM 33 in S4 and the voltage-current characteristic determined in S5. This base voltage Vb corresponds to a secondary transfer partial voltage (transfer voltage for the electrical resistance of the secondary transfer portion N2). The control of acquiring information on the electrical resistance of the secondary transfer portion N2 and setting the transfer voltage in this manner is called ATVC control (Active Transfer Voltage Control). Note that the secondary transfer power source 76 may apply the target current Itarget to the secondary transfer outer roller 45b by constant current control, detect the voltage value at that time by the voltage detection sensor 76a, and set the detected voltage as the voltage value Vb. Information for determining the recording material partial voltage (transfer voltage for the electrical resistance of the recording material S) Vp is stored in the ROM 32. This information is stored as table data showing the relationship between the moisture amount of the atmosphere and the recording material voltage Vp for each paper type category classified by the basis weight of the recording material S. For example, such table data is obtained in advance by experiments for a representative brand of recording material S selected for each basis weight category of the recording material S. FIG. 6 shows an example of the table data. The recording material voltage Vp may vary depending on the surface properties of the recording material S in addition to the basis weight of the recording material S. Therefore, the table data may be set for each paper type category classified based on the surface properties of the recording material S. The control unit 30 can obtain the moisture amount of the atmosphere based on the environmental information (temperature and humidity) detected by the temperature sensor 71 and the humidity sensor 72. The control unit 30 obtains the recording material voltage Vp from the table data based on the job information obtained in S1 and the environmental information obtained in S3. If an adjustment value ΔV is set by the secondary transfer voltage adjustment mode (or recording material registration mode) described later, the control unit 30 obtains the adjustment value ΔV. As will be described later, this adjustment value ΔV is stored in the ROM 32 in the adjustment mode (or the recording material registration mode).The control unit 30 calculates Vb+Vp+adjustment value ΔV by adding the above Vb, Vp, and adjustment value ΔV as the secondary transfer voltage Vtr to be applied from the secondary transfer power source 76 to the outer secondary transfer roller 45b when the recording material S is passing through the secondary transfer unit N2, and writes the result to the RAM 33. Note that the secondary transfer voltage Vtr when the adjustment value ΔV is ±0V is defined as the standard secondary transfer voltage. The standard secondary transfer voltage Vtr (=Vb+Vp) corresponds to the secondary transfer voltage when the adjustment value ΔV is "±0V" that is applied to the outer secondary transfer roller 45b when transferring a patch with identification information (patch number) "0" in the adjustment chart described later to the recording material S.

[0061] Next, the control unit 30 executes image formation, sends the recording material S to the secondary transfer unit N, and applies the secondary transfer voltage Vtr determined as described above to perform secondary transfer (S7). Thereafter, the control unit 30 repeats the process of S7 until all images of the job have been transferred to the recording material S and output (S8).

[0062] Incidentally, with regard to the primary transfer portion N1 as well, the same ATVC control as described above may be performed from the start of a job until the toner image is transported to the primary transfer portion N1.

[0063] 5. Overview of Secondary Transfer Voltage Adjustment Mode and Recording Material Registration Function Next, an outline of the secondary transfer voltage adjustment mode (simplified adjustment mode) using an adjustment chart and the recording material registration function will be described.

[0064] Depending on the type and condition of the recording material S used by the user, the electrical resistance of the recording material S may differ from the electrical resistance of the representative recording material S held in the table data described above. In that case, if the recording material distribution voltage Vp of the table data described above is used, there is a possibility that proper transfer cannot be performed. That is, in order to suppress the occurrence of image defects when the toner on the intermediate transfer belt 44b is transferred to the recording material S, it is necessary to apply an appropriate secondary transfer voltage Vtr to the secondary transfer outer roller 45b. If the electrical resistance of the recording material S used by the user is higher than the electrical resistance of the recording material S held as the table data, the current required to transfer the toner may be insufficient, and image defects such as low density and transfer voids may occur. In that case, it is desirable to set the secondary transfer voltage Vtr higher. Also, if the recording material S absorbs moisture and the electrical resistance of the recording material S is lower than the electrical resistance of the recording material S held as the table data, the recording material S may be in a state where a discharge phenomenon is likely to occur, and image defects such as whiteouts due to abnormal discharge may occur. In that case, it is desirable to set the secondary transfer voltage Vtr lower.

[0065] Therefore, the image forming apparatus 1 of this embodiment is provided with an adjustment mode for obtaining an appropriate adjustment value ΔV in order to set an appropriate secondary transfer voltage that can suppress the occurrence of image defects for each individual recording material S that the user actually uses. In this embodiment, in the adjustment mode, a predetermined adjustment chart including a plurality of solid density images and a plurality of halftone density images as a plurality of patches (test images) is output. The adjustment chart is output by transferring a plurality of patches to the recording material S with the secondary transfer voltage Vtr switched for each patch. The transferability of the plurality of patches is changed by applying a secondary transfer voltage to the outer secondary transfer roller 45b, which is obtained by adding or subtracting an adjustment value ΔV that is changed by a predetermined change width with respect to the standard secondary transfer voltage Vtr, to the plurality of patches, and the patches are transferred to the recording material S. In order to select a patch (adjustment value ΔV), identification information (such as a numerical value) is also transferred to the adjustment chart in association with each patch, and the secondary transfer voltage is changed so as to correspond to this identification information. A patch with the optimal transferability is selected from the patches transferred to the recording material S with different secondary transfer voltages Vtr, and the corresponding adjustment value ΔV is obtained. In this embodiment, in the adjustment mode, the user can visually check the adjustment chart (or with a colorimeter) and select the adjustment value ΔV, and the control unit 30 presents a recommended adjustment value ΔV based on the density information (density data) of each patch obtained by reading the adjustment chart with the reading device 80.

[0066] Here, in the image forming apparatus 1, for example, a representative brand of recording material S is selected in advance, and image forming conditions (transfer conditions, fixing conditions, etc.) are set for each type of recording material S (for example, paper type category). The user operates the image forming apparatus 1 to specify the recording material S to be used from among the types of recording material S set in advance, and perform image formation. However, as described above, there are a great many types of recording material S in circulation.

[0067] Therefore, the image forming apparatus 1 is provided with a recording material registration function so that, for example, a user can perform image formation under appropriate image formation conditions for a new recording material S. The recording material registration function, for example, selects and sets a corresponding type of recording material S (for example, a type that matches the paper type category) from among the types of recording material S previously set in the image forming apparatus 1 as the type of recording material S to be newly set in the recording material cassette 91 of the feeding unit 90.

[0068] However, there may be cases where the user does not have sufficient information about the recording material S, such as when the user does not have sufficient knowledge about the recording material S. For example, the user may mistakenly recognize the recording material S, which corresponds to cardboard as a type of recording material S preset in the image forming apparatus 1, as plain paper. In this case, the user may select the wrong type of recording material S in the recording material registration function. If the type of recording material S selected by the user differs from the actual type of recording material S, the transfer conditions and fixing conditions may not be appropriate, and image defects may occur.

[0069] In addition, for example, the recording material S that the user wishes to newly register may have an electrical resistance that is different from the standard value. Therefore, for example, for the recording material S that the user wishes to newly register, it may be desirable to adjust (change) the secondary transfer voltage setting from the standard setting that is set in advance in the image forming apparatus 1.

[0070] As described above, the image forming apparatus 1 can automatically determine the type of the recording material S using a sensor and set the image forming conditions according to the determination result. However, even if the type of the recording material S can be determined using a sensor, for example, the recording material S may have characteristics (surface properties or electrical resistance) outside the specifications, or the electrical resistance of the recording material may differ from the standard value due to the storage condition (moisture content) of the recording material. Therefore, even if the image forming apparatus 1 has a function of setting the image forming conditions according to the type of the recording material S determined using a sensor, it may be desirable to adjust (change) the setting of the secondary transfer voltage from the standard setting previously set in the image forming apparatus 1 according to the type of the recording material S. For example, even if the recording materials S are determined to be the same type based on the basis weight of the recording materials S, if the recording material S has a low surface smoothness, for example, when the toner is transferred at the secondary transfer portion N2, the toner is difficult to transfer at the recessed portion of the recording material S. This makes it difficult to transfer the toner evenly, and density unevenness may occur. Furthermore, the moisture content of the recording material S changes depending on the storage environment of the recording material S and the environment in which the image forming apparatus 1 is used, which changes the electrical characteristics of the recording material S. Thus, even when the basis weight and surface properties of the recording material S can be determined using a sensor, there are cases in which it is desirable to adjust the secondary transfer voltage.

[0071] It is conceivable that a user who does not have sufficient information about the recording material S can use a function to automatically determine the type of the recording material S using a sensor provided in the image forming apparatus 1 when adjusting the secondary transfer voltage. However, if the type of the recording material S is determined using the sensor first and then the secondary transfer voltage is adjusted in the adjustment mode for the determined type of recording material S, this may impose a burden on the user. In addition, since the recording material S used to determine the type of the recording material S passes through the fixing device 46 and is discharged from the image forming apparatus 1, it is generally not suitable for reuse as a recording material S for outputting a good image due to changes in the moisture content, etc. Therefore, if the type of the recording material S is determined using the sensor as described above and then the secondary transfer voltage is adjusted in the adjustment mode, different recording materials S are required for determining the type of the recording material S and for adjusting the secondary transfer voltage, and the amount of "wasted paper" that is not used for outputting an image increases.

[0072] Therefore, in this embodiment, a recording material registration mode in which the recording material S can be registered and the secondary transfer voltage can be adjusted simultaneously is provided in the image forming apparatus 1. Note that the image forming apparatus 1 in this embodiment is also capable of separately executing a secondary transfer voltage adjustment mode that does not involve the registration of the recording material S.

[0073] 6. Adjustment Chart Next, the adjustment chart (adjustment image, test page) output in the adjustment mode (or recording material registration mode) in this embodiment will be described. Figures 7 and 8 are schematic diagrams of the adjustment chart 100 in this embodiment. In this embodiment, in the adjustment mode (or recording material registration mode), the adjustment chart 100 shown in Figure 7 or 8 is output according to the size of the recording material S used.

[0074] 7 shows an adjustment chart 100 to be output when the length of the recording material S in the conveying direction is 420 to 487 mm, and as an example, shows an adjustment chart in the case where 11 patch sets (described later) corresponding to 11 stages of secondary transfer voltages changed by a predetermined change width are formed. FIG. 8 shows an adjustment chart 100 to be output when the length of the recording material S in the conveying direction is 210 to 419 mm, and as an example, shows an adjustment chart in the case where 10 patch sets corresponding to 10 stages of secondary transfer voltages changed by the same change width as above are formed. In this embodiment, the adjustment chart can be output on both sides of the recording material S even in the adjustment mode (or recording material registration mode) so that the secondary transfer voltages during secondary transfer to the front side (first side) and back side (second side) in double-sided image formation can be adjusted respectively. 7 and 8 respectively show an adjustment chart when an adjustment chart (hereinafter also referred to as a "single-sided chart") is formed on one side of the recording material S, and an adjustment chart (hereinafter also referred to as a "double-sided chart") is formed on both sides of the recording material S. The double-sided chart is formed by double-sided image formation using the above-mentioned double-sided conveying unit 11.

[0075] Here, the size of the recording material S is indicated by recording material width (length in the main scanning direction) x recording material length (length in the sub-scanning direction). The recording material width is the length in a direction (width direction) substantially perpendicular to the conveying direction of the recording material S when passing through the secondary transfer portion N2. The recording material length is the length in a direction substantially parallel to the conveying direction of the recording material S when passing through the secondary transfer portion N2.

[0076] Fig. 7 shows a large size adjustment chart (hereinafter also referred to as "large chart") 100L (100La, 100Lb) that is output when using a large size recording material S such as A3 (297mm x 420mm) or ledger (approximately 280mm x 432mm). Fig. 7(a) shows a large chart 100La when outputting a single-sided chart (or the first side when outputting a double-sided chart). Fig. 7(b) shows a large chart 100Lb on the second side when outputting a double-sided chart.

[0077] Fig. 8 shows small size adjustment charts (hereinafter also referred to as "small charts") 100S (100Sa, 100Sb) that are output when using small size recording material S such as A4 landscape (297mm x 210mm) or letter landscape (approximately 280mm x 216mm). Figs. 8(a) and (b) respectively show the first and second small charts 100Sa when a single-sided chart is output (or the first side when a double-sided chart is output). Figs. 8(c) and (d) respectively show the first and second small charts 100Sb on the second side when a double-sided chart is output.

[0078] In this embodiment, the adjustment chart 100 has a patch set in which one blue solid patch 101, one black solid patch 102, and two halftone patches 103 are arranged in the width direction. In the example of FIG. 7, the large chart 100L has eleven sets of the width direction patch sets 101-103 arranged in the transport direction. In the example of FIG. 8, the small chart 100S has ten sets of the width direction patch sets 101-103 arranged in the transport direction. In this embodiment, the halftone patch 103 is a gray (black halftone) patch. Here, the solid image is an image of the maximum density level. In this embodiment, the blue solid, which is a secondary color solid image, is a superposition of 100% magenta (M) toner and 100% cyan (C) toner, and the toner loading amount of the blue solid is 200%. Moreover, a halftone image is an image with a toner amount of 10 to 80%, where the toner amount of a solid image is 100%.

[0079] In this embodiment, the adjustment chart 100 is provided with patch identification information 104 that is associated with each of the patch sets 101 to 103 and that identifies the setting value of the secondary transfer voltage applied to each of the patch sets. The patch identification information 104 is set to a value corresponding to the adjustment value ΔV of the secondary transfer voltage. In the example of FIG. 7, eleven pieces of patch identification information 104 (11 pieces from −5 to 0 to +5) corresponding to eleven stages of secondary transfer voltage settings are arranged on the large chart 100L. In the example of FIG. 8, ten pieces of patch identification information 104 (five pieces from −4 to 0 on the first sheet and five pieces from +1 to +5 on the second sheet) corresponding to ten stages of secondary transfer voltage settings are arranged on the small chart 100S. In addition, the adjustment chart 100 may be provided with front / back identification information 105 on at least one of the front side (first side) or back side (second side) of the recording material S, which indicates at least one of the front side (first side) or back side (second side) of the recording material S.

[0080] In this embodiment, the blue solid patch 101 and the black solid patch 102 are each a square of 25.7 mm×25.7 mm (one side is approximately parallel to the width direction). In this embodiment, the halftone patches 103 at both ends in the width direction each have a width of 25.7 mm in the transport direction, and extend to the very end of the adjustment chart 100 in the width direction (there may be a margin). In this embodiment, the interval between the patch sets 101 to 103 in the transport direction is 9.5 mm. The secondary transfer voltage is switched at the timing when the part on the adjustment chart 100 corresponding to this interval passes through the secondary transfer portion N2. In this embodiment, the patch sets 101 to 103 of the adjustment chart 100 are sequentially transferred from the upstream side to the downstream side in the transport direction of the recording material S when the adjustment chart 100 is formed, using a plurality of secondary transfer voltages that are different so that the absolute values ​​are sequentially increased. However, the present invention is not limited to such an embodiment. Each patch set 101 to 103 of the adjustment chart 100 may be transferred sequentially from the upstream side to the downstream side in the transport direction of the recording material S when the adjustment chart 100 is formed, using multiple secondary transfer voltages whose absolute values ​​are different from each other so that they become smaller in sequence.

[0081] The maximum size of the recording material S that can be used in the image forming apparatus 1 of this embodiment is 13 inches (about 330 mm) x 19.2 inches (about 487 mm), and the large chart 100L shown in FIG. 7 corresponds to this size of recording material S. When the size of the recording material S is 13 inches x 19.2 inches or less and A3 (297 mm x 420 mm) or more, an adjustment chart corresponding to image data cut from the image data of the large chart 100L shown in FIG. 7 according to the size of the recording material S is output. At this time, in this embodiment, the image data is cut according to the size of the recording material S based on the center of the leading edge. That is, the leading edge of the recording material S in the conveying direction and the leading edge of the large chart 100L in the conveying direction (the upper edge in the figure) are aligned, and the center of the recording material S in the width direction and the center of the large chart 100L in the width direction are aligned, and the image data is cut. Also, in this embodiment, the image data is cut so that a margin of 2.5 mm is provided at the ends (both ends in the width direction and both ends in the conveying direction in this embodiment). When a recording material S having a width smaller than 13 inches is used, the widthwise size of the halftone patches 103 at the ends in the widthwise direction becomes smaller. When the number of patch sets (the number of stages of secondary transfer voltage) is greater than that in the example shown in Fig. 7, the number of adjustment charts 100L as shown in Fig. 7 is increased, and for example, a patch set corresponding to the adjustment value ΔV of "±0V" is formed on the middle number of the patch sets.

[0082] In this embodiment, when a recording material S smaller than A3 (297 mm x 420 mm) is used, a small chart 100S as shown in FIG. 8 is output. The small chart 100S in FIG. 8 corresponds to a size smaller than A5 (vertical feed) to A3 (297 mm x 420 mm) (i.e., a length in the conveying direction of 210 to 419 mm). In the width direction, the halftone patch 103 becomes smaller according to the size of the recording material S. In the case of a recording material S with a length in the conveying direction of 210 to 419 mm, only five patch sets can be formed in the conveying direction on one sheet. Therefore, in order to increase the number of patches, the adjustment chart is divided into two sheets, and a total of ten patch sets are formed, five sets of -4 to 0 and five sets of +1 to +5. In the small chart 100S, the patch set of -5 in the large chart 100L is omitted. In addition, when the number of patch sets (number of stages of secondary transfer voltage) is greater than the example shown in Figure 8, the number of sets of adjustment charts 100S consisting of two sheets as shown in Figure 8 is increased, and a patch set corresponding to the adjustment value ΔV of "±0V" is formed on the number of sheets that corresponds to the middle of the number of patch sets, for example.

[0083] In addition to standard sizes, the adjustment chart 100 may be output using recording material S of any size (free size) by the operator specifying the size through the operation unit 70 or the external device 200, for example.

[0084] Here, one adjustment chart 100 may be formed on one side of one sheet of recording material S, or may be formed separately on one side of each of multiple sheets of recording material S. That is, one adjustment chart 100 may be one set of adjustment charts having one set of patch groups in which the secondary transfer voltage (test voltage) is changed stepwise. In the example of FIG. 7, the large chart 100La (first side) and the large chart 100Lb (second side) each correspond to one adjustment chart. Also, in the example of FIG. 8, the first and second small charts 100Sa (first side) correspond to one adjustment chart as a whole. Similarly, the first and second small charts 100Sb (second side) correspond to one adjustment chart as a whole.

[0085] 7. Recording material registration mode Next, the recording material registration mode in this embodiment will be described. FIG. 9 is a flow chart showing an outline of the procedure of the adjustment mode in this embodiment. In the recording material registration mode, for example, a recording material S to be newly used by the user or a recording material S having a different unused state (such as moisture content) is selected from among the types of recording material S preset in the image forming apparatus 1, and stored in the ROM 32 of the control unit 30. Also, in the recording material registration mode, appropriate secondary transfer conditions are obtained according to the type and state of the recording material S, and stored in the ROM 32 of the control unit 30. The recording material S may be registered in association with, for example, the recording material cassette 91 of the feeding unit 90 in which the recording material S is accommodated.

[0086] For example, when the user sets the recording material S in the feeding unit 90, the control unit 30 causes the display unit 70a of the operation unit 70 to display a recording material registration screen 700 that enables the user to start a recording material registration mode as shown in FIG. 10A (S101). The control unit 30 can detect that the recording material S has been set based on a signal from a sensor that detects the opening and closing of the recording material cassette 91 (or the manual feed tray) or a sensor that detects the recording material S provided in the recording material cassette 91 (or the manual feed tray). Note that the control unit 30 may be configured to display the recording material registration screen 700 as shown in FIG. 10A on the display unit 70a of the operation unit 70 in response to a user's operation on a main screen (not shown) displayed on the display unit 70a of the operation unit 70.

[0087] When a user operates a recording material registration button 701 on a recording material registration screen 700 shown in Fig. 10(a) to input a start command, the control unit 30 starts the recording material registration mode and transitions the recording material registration screen 700 to a display as shown in Fig. 10(b) (S102). On the recording material registration screen 700 shown in Fig. 10(b), a recording material type display section 702 for displaying a paper type category ("paper classification" in the figure) to be determined as described later is displayed blank. Also, voltage setting display sections 703 (first side) and 704 (second side) for displaying an adjustment value ΔV of the secondary transfer voltage (more specifically, a patch number indicating the adjustment value ΔV) to be determined as described later are displayed blank.

[0088] When the control unit 30 starts the recording material registration mode, the control unit 30 feeds the recording material S from the recording material cassette 91 (or manual feed tray) of the feeding unit 90 in which the recording material S has been set by the user, and obtains the detection results of the surface property and basis weight of the recording material S by the recording material discrimination unit 300. Then, the control unit 30 discriminates the type of the recording material S (e.g., paper type category) based on the detection results (S103). The control unit 30 also stores the discrimination results of the type of the recording material S in the ROM 32 (S104). Next, the control unit 30 transfers patches to the recording material S whose surface property and basis weight have been detected by the recording material discrimination unit 300 while varying the secondary transfer conditions, to form an adjustment chart (S105), and outputs the adjustment chart from the image forming apparatus 1 after fixing processing (S106).

[0089] Here, as described above, in order to appropriately adjust the secondary transfer voltage using the adjustment chart, it is desired that the transfer current flowing in response to the secondary transfer voltage when transferring each patch is swung from a current value before the transferability rises to a current value after the transferability rises. In this embodiment, the range of the secondary transfer voltage is set to a wide range so that a sufficient range of secondary transfer voltage can be applied regardless of the type of recording material S when the adjustment chart is output. In this embodiment, the above-mentioned ATVC control is performed before the recording material S on which the adjustment chart is formed reaches the secondary transfer portion N2, and the range of the secondary transfer voltage is set to a sufficient range according to the result (see Example 2 for details). That is, as described above, the base voltage Vb corresponding to the target transfer current Itarget can be determined by the ATVC control. Also, for example, based on the recording material distribution voltage Vp for all types of recording materials S set in the image forming apparatus 1, the range of the secondary transfer voltage when the adjustment chart is output is set to be sufficiently wide, for example, from (Vb+0) [V] to (Vb+4000V) [V]. In this case, the difference between the minimum applied voltage and the maximum applied voltage is 4000V, and if the change width of the adjustment value ΔV, which is incremented by 4000V at equal voltage intervals, is set to, for example, 200V, the number of stages of the secondary transfer voltage will be 20. Also, in this case, for the above-mentioned large chart 100L, the number of sheets of recording material S required to output the adjustment chart will be two. In this way, the secondary transfer voltage is switched in stages in response to the pattern image (multiple patches) for adjusting the secondary transfer voltage, and the adjustment chart is output.

[0090] In this embodiment, when the adjustment chart is formed on multiple sheets of recording material S, the type of at least one of the recording materials S, for example, the type of the recording material S that is fed first, can be determined using the recording material determination unit 300.

[0091] Next, the output adjustment chart is set in the reading device 80 by the operator, and density information of each patch of the adjustment chart is read by the reading device 80 under the control of the control unit 30 (S107). For example, density information (brightness information) of a solid blue patch is read by the reading device 80 and stored in the RAM 33. At this time, the control unit 30 can control the recording material registration screen 700 or the like to display a message urging the operator to set the adjustment chart in the reading device 80. In addition, the control unit 30 can control the operation unit 70 to start reading the adjustment chart 100 by the user operating a start button (not shown).

[0092] Next, the control unit 30 determines an appropriate secondary transfer condition, that is, a recommended adjustment value ΔV of the secondary transfer voltage (S108). The process itself for determining the recommended adjustment value ΔV of the secondary transfer voltage can be any available process, such as a known process. For example, the control unit 30 acquires RGB luminance data (8 bits) of a solid blue patch corresponding to each adjustment value ΔV, which is read from the adjustment chart and stored in the RAM 33. The control unit 30 also calculates the average luminance value of each patch using the acquired luminance data. This allows information indicating the relationship between the adjustment value ΔV (more specifically, the patch number indicating the adjustment value ΔV) and the average luminance value of the patch, as shown in FIG. 13, to be acquired. Then, the control unit 30 can extract, for example, the adjustment value ΔV at which the average luminance value is minimum (the density is maximum) based on this relationship, and determine it as the recommended adjustment value ΔV of the secondary transfer voltage. In addition, for example, an adjustment value ΔV in a brightness stable region where the brightness difference between adjacent adjustment values ​​ΔV is below a predetermined value, or an adjustment value ΔV where the standard deviation of the average brightness value for a predetermined number of patches is minimized, may be extracted and determined as the recommended adjustment value ΔV for the secondary transfer voltage.

[0093] The control unit 30 also stores the determination result of the recommended adjustment value ΔV of the secondary transfer voltage in the ROM 32 (S109). Furthermore, as shown in Fig. 11(a), the control unit 30 displays the determined type of recording material S (e.g., paper type category) in the recording material type display unit 702 on the recording material registration screen 700, and displays the found recommended adjustment value ΔV of the secondary transfer voltage (more specifically, the patch number indicating the adjustment value ΔV) in the voltage setting display units 703 (first side) and 704 (second side) (S110).

[0094] Here, the user may be allowed to visually check the output adjustment chart (or with a colorimeter) and modify the adjustment value ΔV determined by the control unit 30. In this case, as shown in FIG. 11(b), edit buttons 706a and 706b that enable the user to modify the adjustment value ΔV (more specifically, the patch number indicating the adjustment value ΔV) are arranged on the recording material registration screen 700. Also, the user may be allowed to modify the type of the determined recording material S. In this case, as shown in FIG. 11(b), edit button 706c that enables the user to modify the type of the recording material S is arranged on the recording material registration screen 700. It may be possible to modify only one of the determined adjustment value ΔV and the determined type of the recording material S.

[0095] Then, as shown in FIG. 11(a) (or FIG. 11(b)), with the final adjustment value ΔV and the type of recording material S displayed on the recording material registration screen 700 so that they can be confirmed, the user operates the registration button 705. This causes the control unit 300 to register (store) the adjustment value ΔV and the type of recording material S in ROM 32 (S111), and terminate the recording material registration mode (S112). Note that the registered recording material information (type of recording material S, adjustment value ΔV) can be edited by the user even after the recording material registration mode has been terminated.

[0096] Thus, in this embodiment, the image forming apparatus 1 includes an image carrier (intermediate transfer belt) 44b that carries a toner image, a transfer member (secondary transfer outer roller) 45b that forms a transfer section (secondary transfer section) N2 that transfers the toner image from the image carrier 44b to the recording material S, an application section (secondary transfer power source) 76 that applies a voltage to the transfer section N2, a feeding section 90 that feeds the recording material S toward the transfer section N2, and a detection section (recording material discrimination unit) 300 that detects an index (in this embodiment, ultrasonic waves transmitted through the recording material S when ultrasonic waves are irradiated onto the recording material S, and light transmitted through the recording material S when light is irradiated onto the recording material S) that correlates with the type of the recording material S upstream of the transfer section N2 in the conveying direction of the recording material S fed from the feeding section 90 and conveyed to the transfer section N2, and obtains the detection result by the detection section 300, The control unit 30 has a control section 30 which controls a first operation of determining the type of recording material S based on the detection result, and a second operation of applying multiple test voltages to the transfer section N2 by the application section 76 to adjust the transfer voltage to be applied to the transfer section N2 by the application section 76 when transferring the toner image to the recording material S, thereby outputting an adjustment chart 100 in which multiple test images are transferred to the recording material S, and an input section (operation section) 70 which inputs instructions to the control section 30, and the control section 30 is capable of controlling the control section 30 to feed the recording material S from the feeding section 90 toward the transfer section N2 in response to a single start instruction input from the input section 70 to perform the first operation, and to perform the second operation of transferring multiple test images to the recording material S whose index has been detected by the detection section 300 in the first operation, thereby outputting the adjustment chart 100. Also, in this embodiment, the image forming apparatus 1 has a storage unit (ROM) 32 that stores information, the first operation is an operation of storing and registering the type of recording material S set in the feeding unit 90 in the storage unit 32 based on the result of determining the type of recording material S, and the start instruction is an instruction to start the first operation. Also, in this embodiment, the detection unit 300 has a first detection unit (basis weight detection unit) 301 that irradiates ultrasonic waves onto the recording material S and detects the ultrasonic waves that pass through the recording material as the index, and a second detection unit (surface property detection unit) 311 that irradiates light onto the recording material S and detects the light that passes through the recording material S as the index.Moreover, in this embodiment, there is provided a reading means (reading device) 80 that acquires information regarding the density of a plurality of test images of the adjustment chart 100, and the control unit 30 can adjust the transfer voltage in the second operation based on the information regarding the density acquired by the reading means 80. Moreover, in this embodiment, the image carrier 44b is an intermediate transfer body that transports the toner image transferred from another image carrier (photosensitive drum) 51 to be transferred to the recording material S at the transfer unit N2.

[0097] As described above, according to this embodiment, in the recording material registration mode, the recording material S is fed to automatically determine the type of the recording material S, and the recording material S is used to output an adjustment chart and adjust the secondary transfer voltage. This eliminates the need to separately determine the type of the recording material S and adjust the secondary transfer voltage, reducing the operator's workload and reducing the amount of "wasted paper" that is not used to output an image. Therefore, according to this embodiment, it is possible to easily adjust the secondary transfer voltage while reducing the operator's workload and reducing the amount of wasted paper.

[0098] In this embodiment, the automatic discrimination of the type of recording material S and the adjustment of the secondary transfer voltage by outputting and reading the adjustment chart are always performed in the recording material registration mode, but it is also possible to perform only the automatic discrimination of the type of recording material S. In this case, for example, as shown in FIG. 12(a), voltage adjustment selection sections 707a and 707b that enable the user to select whether or not to output the adjustment chart are provided on the recording material registration screen 700, so that the user can select whether or not to output the adjustment chart when starting the recording material registration mode. In this way, the input section 70 can input an instruction to the control section 30 to execute the first operation and not execute the second operation in response to the start instruction.

[0099] In addition, in this embodiment, a double-sided chart is output as the adjustment chart in the recording material registration mode, but it is also possible to select whether to output a single-sided chart or a double-sided chart. In this case, for example, as shown in Fig. 12(b), chart selection sections 708a and 708b that enable selection between a single-sided chart and a double-sided chart are provided in the recording material registration screen 700, so that the user can select which adjustment chart to output when starting the recording material registration mode.

[0100] [Example 2] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are given the same reference numerals as those of embodiment 1, and detailed explanations are omitted.

[0101] 1. Overview of this embodiment As described above, in order to appropriately adjust the secondary transfer voltage using the adjustment chart, it is desirable that the transfer current that flows corresponding to the secondary transfer voltage when transferring each patch varies from a current value before transferability is established to a current value after transferability is established.

[0102] Here, if the central value (central voltage) of the secondary transfer voltage that is changed when the adjustment chart is output is not appropriately set in accordance with the recording material distribution voltage Vp, which differs for each type (electrical resistance) of the recording material S, then in order to include the appropriate secondary transfer voltage adjustment value ΔV in one adjustment chart, the number of recording materials S required to output that one adjustment chart may increase.

[0103] In addition, when the electrical resistance of the recording material S used is different, if the change width of the adjustment value ΔV of the secondary transfer voltage switched for each patch is constant, the range of the current fluctuating in the adjustment chart may not be appropriate, and it may be difficult to select an appropriate secondary transfer voltage. FIG. 14 is a graph showing the transfer current that flows when transferring each patch when a low-resistance recording material S and a high-resistance recording material S are used when outputting the adjustment chart shown in FIG. 7. The secondary transfer voltage when the adjustment value ΔV of patch number "0" is "±0V" is the standard secondary transfer voltage for the recording material S used. The vertical axis of FIG. 14 indicates the transfer current that flows when the adjustment chart is output while switching the secondary transfer voltage with a change width of 75V / 1 level as an example. As shown in FIG. 14, when the adjustment chart is output with the same change width of the secondary transfer voltage, when a high-resistance recording material S is used, the difference in the transfer current that flows when transferring each patch is smaller than when a low-resistance recording material S is used, and there is no difference in the transferability for each patch. Therefore, under these conditions, when a high resistance recording material S is used, it becomes more difficult to determine and select an appropriate secondary transfer voltage using the adjustment mode than when a low resistance recording material S is used.

[0104] Therefore, in this embodiment, in the recording material registration mode, the result of discrimination of the type of recording material S using the recording material discrimination unit 300 is reflected in the setting of the output operation of the adjustment chart. This makes it possible to set more appropriate secondary transfer conditions while reducing the number of sheets of recording material S required to output the adjustment chart.

[0105] 2. Recording material registration mode Next, the recording material registration mode in this embodiment will be described. Fig. 15 is a flow chart showing an outline of the procedure of the adjustment mode in this embodiment. In the procedure of Fig. 15, the same process as that in the procedure of Fig. 9 described in the first embodiment will not be described as appropriate.

[0106] The processes in S201 to S204 in FIG. 15 are similar to the processes in S101 to S104 in FIG.

[0107] In this embodiment, the control unit 30 determines the secondary transfer conditions in the output operation of the adjustment chart based on the type of the recording material S (for example, paper type category) that was determined in S203 and stored in the ROM 32 in S204 (S205). First, the control unit 30 sets the center value (center voltage) of the secondary transfer voltage to be changed when the adjustment chart is output according to the recording material distribution voltage Vp corresponding to the type of the recording material S determined using the recording material determination unit 300. That is, in this embodiment, the above-mentioned ATVC control is performed before the recording material S forming the adjustment chart reaches the secondary transfer portion N2, and the base voltage Vb corresponding to the target transfer current Itarget is determined based on the acquired voltage-current characteristic of the secondary transfer portion N2. In addition, from the table value of the recording material distribution voltage Vp that is set in advance according to the type of the recording material S, the one corresponding to the identified type of the recording material S is acquired. As a result, the standard secondary transfer voltage Vtr (=Vb+Vp) is determined when the adjustment value ΔV of the patch number "0", which is the center voltage when the adjustment chart is output, is "±0V". Furthermore, the control unit 30 sets the change width of the adjustment value ΔV of the secondary transfer voltage based on the type of the recording material S identified by the recording material identification unit 300. The change width of this adjustment value ΔV is set in advance for each type of recording material S and stored in the ROM 32. In this embodiment, the change width of the adjustment value ΔV is set for each type of recording material S so that an adjustment chart can be output using one sheet of recording material S for a large chart 100L as shown in FIG. 7, or two sheets of recording material S for a small chart 100S as shown in FIG. 8. Then, the control unit 30 forms an adjustment chart under the determined secondary transfer conditions (S206), and outputs the adjustment chart from the image forming apparatus 1 after fixing processing (S207).

[0108] In this way, the range of the secondary transfer voltage when outputting the adjustment chart is limited by setting the secondary transfer conditions based on the type of recording material S identified by the recording material identification unit 300. Therefore, the adjustment value ΔV can be determined with high accuracy, and the secondary transfer voltage can be adjusted with a small number of recording materials S.

[0109] For example, when the recording material voltage Vp is about 2000V and the basis weight is 250g / m2 Consider a case where a user mistakenly recognizes the recording material S as plain paper when a thick paper of 800V is set in the feeding section 90. If the recording material voltage Vp of plain paper is stored in the ROM 32 as 800V, the voltage difference from the correct recording material voltage Vp is about 1200V, and an image defect may occur. Then, for example, when an image defect occurs, if the user adjusts the secondary transfer voltage, since plain paper is specified as the type of recording material S, the central voltage of patch number "0" is set using 800V, which is the recording material voltage Vp of plain paper, when the adjustment chart is output. In this case, if the change width of the adjustment value ΔV is, for example, 100V, even with patch number "+5", the secondary transfer voltage can only be applied up to 1300V (in the case of large chart 100L). In this case, a second adjustment chart is required to adjust the secondary transfer voltage appropriately. For example, in the second adjustment chart, a secondary transfer voltage of 1400 to 2400V can be applied (in the case of large chart 100L), so that the transferability of about 2000V can be confirmed. In contrast, in this embodiment, the type of recording material S is identified by the recording material discrimination unit 300 upstream of the secondary transfer portion N2 in the conveying direction of the recording material S. Then, since the recording material S is determined to be thick paper, the center voltage of patch number "0" is set using 2000V, which is the recording material distribution voltage Vp of thick paper, when the adjustment chart is output. As a result, it is possible to apply a secondary transfer voltage of 1500 to 2500V in the adjustment chart formed on one sheet of recording material S and check the transferability (in the case of large chart 100L). Note that, although an example related to the basis weight of the recording material S has been described here, the center voltage when the adjustment chart is output can also be changed depending on the type of recording material S based on the surface property of the recording material S. For example, coated paper has a tendency to have a higher electrical resistance than uncoated paper due to the presence of a coating material. Therefore, it may be desirable to set a higher central voltage (larger absolute value) for coated paper than for uncoated paper. From another perspective, rough paper tends to be more difficult to transfer toner to than plain paper due to its uneven surface. Therefore, it may be desirable to set a higher central voltage (larger absolute value) for rough paper than for plain paper.

[0110] Also, as described above, it is desirable to vary the change range of the adjustment value ΔV depending on the type of recording material S. Specifically, it is desirable to reduce the change range of the adjustment value ΔV for recording materials S with low electrical resistance (low recording material shared voltage Vp). Also, it is desirable to increase the change range of the adjustment value ΔV for recording materials S with high electrical resistance (high recording material shared voltage Vp). For example, the change range of the adjustment value ΔV can be set to 75V for thin paper, 150V for plain paper, and 300V for thick paper and coated paper. Since recording materials S with high electrical resistance have high electrical resistance to begin with, by increasing the change range of the adjustment value ΔV, the current flowing through the secondary transfer portion N2 can be sufficiently changed to change the transferability of each patch. If the change range of the adjustment value ΔV is small for high-resistance recording materials S, the transfer current that actually flows cannot be changed significantly, so there is a possibility that the optimal adjustment value ΔV cannot be found in the adjustment chart formed on one sheet of recording material S.

[0111] In this embodiment, both the central voltage when the adjustment chart is output and the change range of the adjustment value ΔV are changed based on the type of recording material S that has been determined, but a corresponding effect can also be obtained by changing only one of these based on the type of recording material S that has been determined.

[0112] The processes in S208 to S213 in FIG. 15 are similar to the processes in S107 to S112 in FIG.

[0113] If the appropriate range of secondary transfer voltage is unknown, there is a method of setting the range of secondary transfer voltage to a wide range when the adjustment chart is output. One method is to set the range of secondary transfer voltage according to the result of ATVC control of secondary transfer unit N2 (see Example 1). By ATVC control, it is possible to determine a base voltage Vb corresponding to a target transfer current Itarget required for transferring toner on intermediate transfer belt 44b to recording material S, based on the voltage-current characteristics of secondary transfer unit N2. Also, for example, it is possible to determine the range of secondary transfer voltage when the adjustment chart is output, based on the minimum and maximum values ​​in a table of recording material distribution voltages Vp for all types of recording material S set in image forming apparatus 1. For example, when the minimum basis weight (e.g., 52 g / m 2 ) recording material S, the recording material voltage Vp is 500V, and the maximum basis weight (for example, 136g / m 2 The recording material voltage Vp for the recording material S of the base voltage Vb or more is 3000V. In this case, the recording material voltage Vp that can be added to the base voltage Vb is 500 to 3000V. The range of the secondary transfer voltage when the adjustment chart is output is a range including Vb+500V and Vb+3000V, for example, (Vb+0) [V] to (Vb+4000V) [V]. In this case, the difference from the minimum applied voltage to the maximum applied voltage is 4000V, and if the change width of the adjustment value ΔV that divides 4000V into equal intervals of voltage is reduced to, for example, 50V, the number of stages of the secondary transfer voltage becomes 80 stages. Also, in this case, for the above-mentioned large chart 100L, the number of sheets of recording material S required to output the adjustment chart will be 7 or more. Therefore, the amount of "wasted paper" increases. On the other hand, if the change width of the adjustment value ΔV is increased to 500V, the number of stages of the secondary transfer voltage decreases and the number of sheets of recording material S required to output the adjustment chart decreases. However, for example, when the voltage-current characteristic of the secondary transfer voltage is a quadratic curve, if the change range of the adjustment value ΔV is large, the accuracy of the obtained transfer current may decrease. In this way, if the discrimination result of the type of recording material S is not reflected in the secondary transfer conditions when the adjustment chart is output, depending on the setting of the adjustment value ΔV, there is a possibility that the amount of wasted paper may increase or the adjustment accuracy may decrease.

[0114] Thus, in this embodiment, the control unit 30 can control the second operation of outputting the adjustment chart 100, which is executed in response to one start instruction input from the input unit 70, to set multiple test voltages based on the discrimination result of the type of the recording material S in the first operation of discriminating the type of the recording material S. The control unit 30 can set the range of multiple test voltages based on the discrimination result. At that time, the control unit 30 can set the range of multiple test voltages so that the absolute value of the center voltage of the range of multiple test voltages when the type of the recording material S indicated by the discrimination result is a second type having a higher electric resistance than the first type is greater than the absolute value of the center voltage of the range of multiple test voltages when the type of the recording material S indicated by the discrimination result is a first type. Furthermore, the control unit 30 can control the second operation to apply multiple test voltages by increasing or decreasing their absolute values ​​stepwise, and can set the change width of the multiple test voltages in one step based on the discrimination result. At this time, the control unit 30 can set the change range so that the change range is larger when the type of recording material S indicated by the discrimination result is a second type having a higher electrical resistance than the first type than when the type of recording material S indicated by the discrimination result is a first type.

[0115] As described above, according to this embodiment, in the recording material registration mode, as in the first embodiment, the recording material S is fed to automatically determine the type of the recording material S, and the adjustment chart is output using the recording material S to adjust the secondary transfer voltage. Therefore, according to this embodiment, it is possible to easily adjust the secondary transfer voltage while reducing the operator's workload and reducing the amount of worn paper. Also, in this embodiment, in the recording material registration mode, the result of automatic determination of the type of the recording material S is reflected in the setting of the output operation of the adjustment chart. As a result, even an operator who does not have sufficient information about the recording material S can easily and appropriately adjust the transfer voltage, and it is possible to further reduce the amount of worn paper compared to the first embodiment.

[0116] In this embodiment, the automatic discrimination result of the type of the recording material S is always reflected in the setting of the output operation of the adjustment chart in the recording material registration mode, but it may be possible to select not to reflect it. In this case, for example, as shown in FIG. 16, the recording material registration screen 700 is provided with valid / invalid selection sections 709a and 709b for validating or invalidating the reflection of the discrimination result of the type of the recording material S in the setting of the output operation of the adjustment chart, so that the user can select either one. In addition, when the discrimination result of the type of the recording material S is not reflected in the setting of the output operation of the adjustment chart, for example, the operation of the recording material registration mode similar to that of the first embodiment may be performed. In this way, the input section 70 can input an instruction to the control section 30 to set a plurality of test voltages to a predetermined setting, regardless of the discrimination result of the type of the recording material S in the first operation, in the second operation executed in response to the start instruction.

[0117] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-mentioned embodiments.

[0118] In the above-described embodiment, the reading device 80 that reads the adjustment chart set by the operator as shown in Fig. 1 is used as the reading device. However, the present invention is not limited to such an embodiment, and the reading device may be a reading device that reads the adjustment chart when the adjustment chart is output from the image forming apparatus 1. For example, as shown in Fig. 17, an in-line image sensor 86 may be provided downstream of the fixing device 46 in the conveying direction of the recording material S. In this case, when the adjustment chart is output from the image forming apparatus 1, the adjustment chart can be read by this image sensor 86 to obtain density information (brightness information) of the patch.

[0119] In the above embodiment, the secondary transfer voltage is adjusted in the recording material registration mode when, for example, the user registers a new recording material S to be used, but the present invention is not limited to such an embodiment. In the adjustment mode in which the secondary transfer voltage is adjusted, the discrimination result of the recording material S using the recording material discrimination unit 300 can be used. For example, in the adjustment mode, the discrimination result of the type of the recording material S using the recording material discrimination unit 300 can be reflected in the setting of the output operation of the adjustment chart, as in the second embodiment. That is, in the adjustment mode, the user specifies the type of the recording material S and adjusts the secondary transfer voltage for that recording material S. However, it is assumed that the user specifies the wrong type of recording material S and performs the adjustment mode when he or she does not have sufficient information about the recording material S. In that case, as described in the second embodiment, it may be difficult to adjust the secondary transfer voltage appropriately. Therefore, in the adjustment mode, the discrimination result of the type of the recording material S using the recording material discrimination unit 300 is reflected in the setting of the output operation of the adjustment chart. As a result, even if a user does not have sufficient information about the recording material S, the secondary transfer voltage can be adjusted appropriately according to the type of the recording material S, as described in the second embodiment.

[0120] In this case, the control unit 30 displays an adjustment screen 800 that allows the adjustment mode to be started on the display unit 70a of the operation unit 70, as shown in FIG. 18. The user operates the recording material selection unit 803 to display the type of recording material S for which the secondary transfer voltage is to be adjusted on the recording material type display unit 702. Then, the user can operate the adjustment button 801 to cause the control unit 30 to start the adjustment mode. When the control unit 30 starts the adjustment mode, it feeds the recording material S on which the adjustment chart is to be formed, and determines the type of the recording material S based on the detection result by the recording material discrimination unit 300. Furthermore, when the type of recording material S specified by the user on the recording material type display unit 702 differs from the type of recording material S determined using the recording material discrimination unit 300, the control unit 30 sets the secondary transfer conditions at the time of outputting the adjustment chart based on the determined type of recording material S. However, similar to the one shown in FIG. 16, it may be possible to select whether or not to reflect the automatic determination result of the type of recording material S in the setting of the output operation of the adjustment chart. In the case where the automatic discrimination result is not reflected, the detection operation by the recording material discrimination unit 300 may not be performed, or the detection operation may be performed without reflecting the automatic discrimination result. The voltage setting display units 804 and 805 of the adjustment screen 800 display the adjustment value ΔV of the secondary transfer voltage (more specifically, a patch number indicating the adjustment value ΔV) obtained in the same manner as in the above-mentioned embodiment. In addition, when the user operates the confirmation button 806, the control unit 30 registers the setting of the secondary transfer voltage in the ROM 32. In addition, the control unit 30 may control so as to correct the type of the recording material S designated by the user in the recording material type display unit 702 to the type of the recording material S discriminated using the recording material discrimination unit 300. In this way, one start instruction input from the input unit 70 may be an instruction to start the second operation of outputting the adjustment chart 100, and the control unit 30 can control so as to set a plurality of test voltages based on the discrimination result of the type of the recording material S in the first operation of discriminating the type of the recording material S in the second operation executed in response to the start instruction.Furthermore, the input section 70 can input to the control section 30 an instruction to set a plurality of test voltages to predetermined settings in the second operation executed in response to the start instruction, regardless of the result of discrimination of the type of the recording material S in the first operation. Alternatively, the input section 70 may be capable of inputting to the control section 30 an instruction to execute the second operation in response to the start instruction, but not to execute the first operation.

[0121] In the above embodiment, the density information (luminance information) is obtained using a blue patch. However, the color of the patch from which the density information (luminance information) is obtained is not limited to blue, and other than blue, secondary colors such as red and green, or a single solid color of YMCK may be used. Halftone density information (luminance information) may also be obtained.

[0122] In the above embodiment, the operations performed by the operation unit 70 as an input unit for inputting instructions to the control unit 30 may be performed by an external device 200 such as a personal computer. In this case, the same settings as those in the above embodiment can be performed via a screen displayed on a display unit of the external device 200 by a driver program of the image forming apparatus 1 installed in the external device 200. In this case, the input / output circuit 34 functions as an input unit for inputting instructions from the external device 200 to the control unit 30.

[0123] Also, in the above embodiment, the configuration in which the secondary transfer voltage is constant voltage controlled has been described, but the secondary transfer voltage may be constant current controlled. In the above embodiment, in the configuration in which the secondary transfer voltage is constant voltage controlled, the secondary transfer voltage is adjusted by adjusting the target voltage when the secondary transfer voltage is applied in the adjustment mode (or recording material registration mode). In the configuration in which the secondary transfer voltage is constant current controlled, the secondary transfer voltage can be adjusted by adjusting the target current when the secondary transfer voltage is applied in the adjustment mode (or recording material registration mode). The change range of the transfer voltage (test voltage) in one step includes the change range of the voltage value when constant voltage control is used, as well as the change range of the current value when constant current control is used.

[0124] The present invention is not limited to tandem type image forming apparatuses, but can also be applied to other types of image forming apparatuses. The image forming apparatus is not limited to full-color image forming apparatuses, but may be monochrome or mono-color image forming apparatuses. The present invention can be implemented in a variety of applications, such as printers, various printing machines, copiers, FAX machines, and multifunction machines.

[0125] The present invention can also be applied to a monochrome image forming apparatus having only one image forming unit, for example. In this case, the present invention can be applied to the transfer unit where a toner image is transferred directly from a photosensitive drum or the like as an image carrier to a recording material. [Explanation of symbols]

[0126] 1. Image forming device 30 Control section 44b Intermediate transfer belt 45b Secondary transfer outer roller 80 Reading device 100 Adjustment Chart 300 Recording material discrimination unit N2 Secondary transfer section S recording material

Claims

1. An image carrier that holds a toner image, A transfer member that forms a transfer section for transferring a toner image from the image carrier to a recording material, An application unit for applying voltage to the transfer unit, A feeding unit that houses the recording material and feeds the recording material toward the transfer unit, A detection unit is provided upstream of the transfer unit in the transport direction of the recording material in the transport path where the recording material is transported, and detects an index from the recording material that correlates with the type of recording material. A memory unit that stores information, A control unit for controlling a first operation and a second operation, wherein in the first operation, the control unit causes the feeding unit to feed recording material, the detection unit to acquire the index from the recording material fed by the feeding unit, and then, based on the detection result of the detection unit, stores the type of recording material set in the feeding unit in the storage unit; and in the second operation, in order to adjust the transfer voltage applied to the transfer unit by the application unit when transferring a toner image to the recording material fed by the feeding unit, the control unit outputs an adjustment chart created by applying a plurality of test voltages to the transfer unit by the application unit and transferring a plurality of test images to the recording material fed by the feeding unit, It has an input unit for inputting instructions to the control unit, The image forming apparatus is characterized in that the control unit can be controlled to execute the first operation in response to a start instruction input from the input unit, and to execute the second operation for outputting the adjustment chart created by transferring the plurality of test images to the recording material in which the indicator was detected by the detection unit in the first operation.

2. The image forming apparatus according to Claim 1, wherein the input unit is capable of selectively inputting a first instruction that instructs to perform the first operation and the second operation, and a second instruction that instructs to perform the first operation and not perform the second operation, wherein the first instruction is one start instruction input from the input unit, and the second instruction is another start instruction input from the input unit.

3. The image forming apparatus according to claim 1, characterized in that the control unit can control the setting of the plurality of test voltages in the second operation performed in response to the one start instruction, based on the detection result of the detection unit in the first operation performed in response to the one start instruction.

4. The image forming apparatus according to claim 3, characterized in that the control unit sets the range of the plurality of test voltages in the second operation performed in response to the one start instruction based on the detection result of the detection unit in the first operation performed in response to the one start instruction.

5. The type of recording material indicated by the detection result of the detection unit in the first operation performed in response to the one start instruction includes a first type and a second type having a higher electrical resistance than the first type, The image forming apparatus according to claim 4, characterized in that the control unit sets the ranges of the plurality of test voltages in the second operation performed in response to the one start instruction such that the absolute value of the center voltage of the plurality of test voltage ranges when the type of recording material is the second type is greater than the absolute value of the center voltage of the plurality of test voltage ranges when the type of recording material is the first type.

6. The image forming apparatus according to claim 1, characterized in that the control unit controls the application of the plurality of test voltages in the second operation performed in response to the one start instruction by gradually increasing or decreasing the absolute value of the corresponding test voltage, and sets the range of change of the plurality of test voltages in one step based on the detection result of the detection unit in the first operation performed in response to the one start instruction.

7. The type of recording material indicated by the detection result of the detection unit in the first operation includes a first type and a second type having a higher electrical resistance than the first type, The image forming apparatus according to claim 6, characterized in that the width of change when the type of recording material is the second type is greater than the width of change when the type of recording material is the first type.

8. The image forming apparatus according to claim 1, wherein the control unit can set the plurality of test voltages based on information about the recording material input by the user, without regard to the detection result of the detection unit in the first operation performed in response to the single start instruction, in the second operation performed in response to the single start instruction.

9. The image forming apparatus according to claim 1, characterized in that the input unit can input a start instruction to the control unit that instructs the second operation to be performed and the first operation not to be performed.

10. The image forming apparatus according to claim 1, characterized in that the detection unit comprises a first detection unit that irradiates a recording material with ultrasonic waves and detects ultrasonic waves transmitted through the recording material as the indicator, and a second detection unit that irradiates a recording material with light and detects light transmitted through the recording material as the indicator.

11. The adjustment chart further comprises a reading means for obtaining information regarding the density of each of the plurality of test images, The image forming apparatus according to claim 1, characterized in that the control unit can adjust the transfer voltage based on the information regarding the concentration obtained by the reading means in the second operation.

12. The image forming apparatus according to claim 1, characterized in that the image carrier is an intermediate transfer body that transports a toner image transferred from another image carrier to a recording material in the transfer unit.

13. The image forming apparatus according to claim 1, characterized in that, when the first operation and the second operation are performed in response to a predetermined start instruction, the control unit can selectively perform an operation in a first mode in which the plurality of test voltages in the second operation performed in response to a predetermined start instruction are set based on the index detected by the detection unit in the first operation performed in response to the predetermined start instruction, and an operation in a second mode in which the plurality of test voltages in the second operation performed in response to a predetermined start instruction are set based on information about the type of recording material input by the user.

14. An image carrier that holds a toner image, A transfer member that forms a transfer section for transferring a toner image from the image carrier to a recording material, An application unit for applying voltage to the transfer unit, A feeding unit that houses the recording material and feeds the recording material toward the transfer unit, A detection unit is provided upstream of the transfer unit in the transport direction of the recording material in the transport path where the recording material is transported, and detects an index correlated with the type of recording material from the recording material supplied from the feeding unit. A control unit for controlling a first operation and a second operation, wherein in the first operation, the control unit causes the feeding unit to feed recording material, and the detection unit to acquire the index from the recording material fed by the feeding unit, and in the second operation, in order to adjust the transfer voltage applied to the transfer unit by the application unit when transferring a toner image to the recording material fed by the feeding unit, the control unit outputs an adjustment chart created by applying a plurality of test voltages to the transfer unit by the application unit and transferring a plurality of test images to the recording material fed by the feeding unit, It has an input unit for inputting instructions to the control unit, The image forming apparatus is characterized in that, in response to a start instruction input from the input unit, the control unit can be controlled to execute the first operation and to execute the second operation for outputting the adjustment chart created by transferring the plurality of test images to the recording material in which the indicator was detected by the detection unit in the first operation.

15. The image forming apparatus according to claim 14, characterized in that the one start instruction instructs the start of the second operation.

16. The image forming apparatus according to claim 15, characterized in that the control unit can control the setting of the plurality of test voltages in the second operation performed in response to the one start instruction, based on the detection result of the detection unit in the first operation performed in response to the one start instruction.

17. The image forming apparatus according to claim 15, characterized in that the control unit sets the range of the plurality of test voltages in the second operation performed in response to the one start instruction based on the detection result of the detection unit in the first operation performed in response to the one start instruction.

18. The type of recording material indicated by the detection result of the detection unit in the first operation performed in response to the one start instruction includes a first type and a second type having a higher electrical resistance than the first type, The image forming apparatus according to claim 17, characterized in that the control unit sets the ranges of the plurality of test voltages in the second operation performed in response to the one start instruction such that the absolute value of the center voltage of the plurality of test voltage ranges when the type of recording material is the second type is greater than the absolute value of the center voltage of the plurality of test voltage ranges when the type of recording material is the first type.

19. The image forming apparatus according to claim 15, characterized in that the control unit controls the application of the plurality of test voltages in the second operation performed in response to the one start instruction by gradually increasing or decreasing the absolute value of the corresponding test voltage, and sets the range of change of the plurality of test voltages in one step based on the detection result of the detection unit in the first operation performed in response to the one start instruction.

20. The type of recording material indicated by the detection result of the detection unit in the first operation includes a first type and a second type having a higher electrical resistance than the first type, The image forming apparatus according to claim 19, characterized in that the width of change when the type of recording material is the second type is greater than the width of change when the type of recording material is the first type.

21. The image forming apparatus according to claim 15, wherein the control unit can set the plurality of test voltages based on information about recording material input by the user, without regard to the detection result of the detection unit in the first operation performed in response to the single start instruction, in the second operation performed in response to the single start instruction.

22. The image forming apparatus according to claim 15, characterized in that the detection unit comprises a first detection unit that irradiates a recording material with ultrasonic waves and detects ultrasonic waves transmitted through the recording material as the indicator, and a second detection unit that irradiates a recording material with light and detects light transmitted through the recording material as the indicator.

23. The adjustment chart further comprises a reading means for obtaining information regarding the density of each of the plurality of test images, The image forming apparatus according to claim 15, characterized in that the control unit can adjust the transfer voltage based on the information regarding the concentration obtained by the reading means in the second operation.

24. The image forming apparatus according to claim 15, characterized in that the image carrier is an intermediate transfer body that transports a toner image transferred from another image carrier to a recording material in the transfer unit.

25. The image forming apparatus according to claim 15, wherein, when the first operation and the second operation are performed in response to a predetermined start instruction, the control unit is capable of selectively performing an operation in a first mode in which the plurality of test voltages in the second operation performed in response to a predetermined start instruction are set based on the index detected by the detection unit in the first operation performed in response to the predetermined start instruction, and an operation in a second mode in which the plurality of test voltages in the second operation performed in response to a predetermined start instruction are set based on information about the type of recording material input by the user.

26. The image forming apparatus according to claim 15, characterized in that the control unit can perform the first operation without performing the second operation in response to a single start instruction.

27. ​​The image forming apparatus according to claim 1, characterized in that the feeding unit includes a cassette for housing recording material.

28. An image carrier that holds a toner image, A transfer member that forms a transfer section for transferring a toner image from the image carrier to a recording material, An application unit for applying voltage to the transfer unit, A cassette containing recording material, A feeding unit that feeds the recording material contained in the cassette toward the transfer unit, A detection unit is provided upstream of the transfer unit in the transport direction of the recording material in a transport path configured to transport the recording material from the cassette, and detects an indicator related to the type of recording material from the recording material. A memory unit that stores information, A control unit capable of performing an adjustment operation to adjust the transfer voltage applied to the transfer unit, by applying multiple test voltages to the transfer unit and outputting an adjustment chart on which multiple test images have been transferred, It has an input unit that inputs instructions to the control unit for performing the adjustment operation, The image forming apparatus is characterized in that the control unit is configured to feed recording material from the cassette in response to the instruction input from the input unit, to have the detection unit acquire the index, to store the type of recording material contained in the cassette in the storage unit, and to transfer the plurality of test images to the recording material on which the index has been detected by the detection unit and output the adjustment chart.

29. The image forming apparatus according to claim 28, characterized in that the control unit can set the plurality of test voltages based on information about the recording material input by the user, regardless of the detection result of the detection unit, in the adjustment operation.

30. The image forming apparatus according to claim 28, characterized in that the control unit can set the plurality of test voltages based on the detection result of the detection unit in the adjustment operation.

31. The image forming apparatus according to claim 28, wherein, when the adjustment operation is performed, the control unit is configured to selectively set the mode to be performed from among a plurality of modes, including a first mode in which the plurality of test voltages are set based on the index detected by the detection unit, and a second mode in which the plurality of test voltages are set based on information about the type of recording material input by the user.

Images