Image forming apparatus

Abstract

To provide an image forming apparatus that outputs a chart for adjustment 400 having a plurality of patch images 403, 404 for adjusting a secondary transfer bias, and even when the chart for adjustment 400 is not placed at the optimal position on a document platen, prevent erroneous detection of an edge of a sheet as edges of the test images.SOLUTION: A test chart 400 has an image for reference position determination 406 for determining the position to start reading patch images 403, 404.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to an image forming apparatus that forms a toner image on a recording material.

Background Art

[0002] In recent years, digital copiers that read a document with a document reading device, perform digital processing on the generated image data, transfer the image data to a printer unit, and print the transferred image data have become mainstream. In an image forming apparatus using an electrophotographic method or the like, a toner image formed on an image carrier such as a photoreceptor or an intermediate transfer member is transferred to a recording material. Transfer of the toner image from the image carrier to the recording material is often performed by applying a transfer voltage to a transfer member such as a transfer roller that abuts against the image carrier to form a transfer portion. Therefore, it has been proposed to provide an adjustment mode for adjusting the set voltage of the transfer voltage according to the recording material actually used for image formation.

[0003] In Patent Document 1, an image forming apparatus having an adjustment mode for adjusting the set voltage of the secondary transfer voltage is proposed. In this adjustment mode, a chart in which a plurality of patches (test images) are formed on one recording material is output with the secondary transfer voltage switched for each patch. Then, the density of each patch is detected, and the optimum secondary transfer voltage conditions are selected according to the detection result. The paper used in this adjustment mode is not necessarily high-quality paper, and paper with irregularities or colored paper may be used.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, test images may include halftone images to confirm the output state of midtones under secondary transfer voltage conditions. In this case, it is necessary to set the edge detection threshold of the patch pattern loosely so that patches formed by the halftone image can be reliably detected. When the edge detection threshold is loose, there is a problem in that when adjusting using colored paper, the edges of the paper are mistakenly detected as the edges of the adjustment patches, making it impossible to properly determine the position of the patches. Therefore, the objective of the present invention is to suppress the misdetection of test images used for adjusting the secondary transfer voltage. [Means for solving the problem]

[0006] The above objective is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides an image forming apparatus comprising: an image carrier that carries a toner image; a transfer member that forms a transfer section for transferring the toner image from the image carrier to a recording material; a power supply that applies a transfer voltage to the transfer member; a control unit that, when not forming an image, applies a plurality of different voltages to the transfer member using the power supply to transfer a plurality of test images from the image carrier to a recording material and outputs a test chart for adjusting the transfer voltage set during image formation; and a reading device that reads the test chart, wherein the transfer voltage set during image formation can be adjusted based on the reading result of the reading device. The control unit is configured to form a reference image on the recording material on which the test chart is formed for determining the starting position of reading the test image by the reading device, and the reading device is configured to determine the starting position of reading the test image based on the position of the reference image when the reference image is detected. [Effects of the Invention]

[0007] According to the present invention, it is possible to suppress the false detection of test images used for adjusting the secondary transfer voltage. [Brief explanation of the drawing]

[0008] [Figure 1]Overview of the image forming apparatus in Example 1 [Figure 2] Block diagram showing the schematic configuration of the control system of the image forming apparatus in Example 1. [Figure 3] This figure shows the schematic configuration of the image reading unit in Example 1. [Figure 4] Example of image data of the adjustment chart output in adjustment mode in Example 1 [Figure 5] (a) Example of how to place a document in the adjustment mode using the document glass (b) Scanned image obtained in the example of Figure 5(a) [Figure 6] (a) An example of placing the document shifted towards the rear end in the sub-scanning direction in the adjustment mode using the document glass. (b) The scanned image obtained in the example of Figure 6(a). [Figure 7] (a) An example of edge detection of the adjustment pattern on the image in Figure 6(b) (b) An example of edge detection of the adjustment pattern when using paper with low whiteness [Figure 8] (a) Example of edge detection of the reference position determination pattern in Example 1 (b) Example of scanning position determination of the adjustment pattern in Example 1 (c) Example of edge detection of the adjustment pattern in Example 1 [Figure 9] (a) An example of placing the document in the sub-scanning direction and rotated 180 degrees in the adjustment mode using the document glass. (b) The scanned image obtained in the example of Figure 9(a). [Figure 10] (a) An example in which edge detection of the reference position determination pattern fails for the image obtained in Figure 9(b) in Example 1. (b) Another example in which edge detection of the reference position determination pattern fails for the image obtained in Figure 9(b) in Example 1. (c) An example in which edge detection of the reference position determination pattern is performed after rotating the read image obtained in Figure 9(b) in Example 1 by 180 degrees. [Figure 11] Flowchart of the adjustment function in Example 1 [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that the following embodiments are not intended to limit the scope of the claims, and not all combinations of features described in these embodiments are necessarily essential to the solutions of the present invention.

[0010] <Examples> Figure 1 is a schematic cross-sectional view of the entire apparatus 1 of this embodiment. The image forming apparatus 2 is a tandem-type full-color printer employing an intermediate transfer method that is capable of forming full-color images using an electrophotographic method. However, the image forming apparatus is not limited to a tandem-type image forming apparatus, and may be an image forming apparatus of other types. Furthermore, the image forming apparatus is not limited to an image forming apparatus capable of forming full-color images, but may be an image forming apparatus capable of forming only monochrome (black and white or monocolor) images. In addition, the image forming apparatus may be an image forming apparatus for various purposes, such as a printer, various printing machines, copiers, fax machines, and multifunction devices.

[0011] As shown in Figure 1, the image forming apparatus 2 includes a paper feeding unit 4, an image forming unit 5, a control unit 30, and an operation unit 70. Although there is only one paper feeding unit 4 in Figure 1, there may be multiple units. Inside, there is also a temperature sensor 71 (Figure 2) capable of detecting the internal temperature and a humidity sensor 72 (Figure 2) capable of detecting the internal humidity. Furthermore, the image forming apparatus 2 can form a four-color full-color image on a recording material (sheet, transfer material) S in response to image information (image signal) from an image reading unit 80 (Figure 3) as a reading means for reading an image on a sheet, or from an external device 200 (Figure 2). Examples of external devices 200 include host devices such as personal computers, or digital cameras and smartphones. The recording material S is on which a toner image is formed, and specific examples include plain paper, synthetic resin sheets that are substitutes for plain paper, cardboard, and overhead projector sheets.

[0012] The image forming unit 5 is capable of forming an image on the recording material S fed from the paper feeding unit 4 and moving within the conveyance path L based on the image information. The image forming unit 5 includes image forming units 50y, 50m, 50c, 50k, toner bottles 41y, 41m, 41c, 41k, exposure devices 42y, 42m, 42c, 42k, an intermediate transfer unit 44, a secondary transfer device 45, and a fixing unit 46. The image forming units 50y, 50m, 50c, 50k form yellow (y), magenta (m), cyan (c), and black (k) images respectively. For elements having the same or corresponding functions or configurations provided corresponding to these four image forming units 50y, 50m, 50c, 50k, the y, m, c, k at the end of the symbol indicating that it is an element for any color may be omitted and described collectively. Note that the image forming apparatus 2 can also form a single-color or multi-color image, such as a black single-color image, using the image forming unit 50 for some of the desired single color or four colors.

[0013] The image forming unit 5 has the following means. First, it has a photosensitive drum 51 which is a drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) as the first image carrier. It also has a charging roller 52 which is a roller-type charging member as the charging means. It also has a developing device 20 as the developing means. It also has a pre-exposure device 54 as the charge removing means. It also has a cleaning blade 55 which is a cleaning member as the photosensitive member cleaning means. The image forming unit 5 forms a toner image on the intermediate transfer belt 44b described later. The image forming unit 5 is unitized integrally as a process cartridge and is detachable from the image forming apparatus main body 10.

[0014] The photosensitive drum 51 can carry and move (rotate) an electrostatic image (electrostatic latent image) and a toner image. In this embodiment, the photosensitive drum 51 is a negatively charged organic photoreceptor (OPC) with an outer diameter of 30 mm. The photosensitive drum 51 has an aluminum cylinder as a substrate and a surface layer formed on its surface. In this embodiment, as the surface layer, it has three layers, namely, an undercoat layer, a photogeneration layer, and a charge transport layer, which are coated and laminated on the substrate in the following order. When the image forming operation is started, the photosensitive drum 51 is rotationally driven in the direction of the arrow in the figure (counterclockwise) at a predetermined process speed (peripheral speed) by a motor (not shown) as a driving means.

[0015] The surface of the rotating photosensitive drum 51 is uniformly charged by a charging roller 52. In this embodiment, the charging roller 52 is a rubber roller that contacts the surface of the photosensitive drum 51 and rotates passively as the photosensitive drum 51 rotates. A charging bias power supply 73 (Fig. 2) is connected to the charging roller 52. The charging bias power supply 73 applies a charging bias (charging voltage) to the charging roller 52 during the charging process.

[0016] The surface of the charged photosensitive drum 51 is scanned and exposed based on image information by an exposure device 42, and an electrostatic image is formed on the photosensitive drum 51. In this embodiment, the exposure device 42 is a laser scanner. The exposure device 42 emits laser light according to the color-separated image information output from the control unit 30 and scans and exposes the surface (outer peripheral surface) of the photosensitive drum 51.

[0017] The electrostatic image formed on the photosensitive drum 51 is developed (visualized) by the development device 20, which supplies toner from the developer, and a toner image is formed on the photosensitive drum 51. In this embodiment, the development device 20 contains a two-component developer (also simply called "developer") comprising non-magnetic toner particles (toner) and magnetic carrier particles (carrier). Toner is supplied to the development device 20 from a toner bottle 41. The development device 20 has a development sleeve 24. The development sleeve 24 is made of a non-magnetic material such as aluminum or non-magnetic stainless steel (aluminum in this embodiment). Inside the development sleeve 24, a magnetic roller, which is a roller-shaped magnet, is fixedly positioned so as not to rotate relative to the main body (developing container) of the development device 20. The development sleeve 24 carries the developer and transports it to the development area facing the photosensitive drum 51. A development bias power supply 74 (Figure 2) is connected to the development sleeve 24. The development bias power supply 74 applies a development bias (developing voltage) to the development sleeve 24 during the development process. In this embodiment, the normal charge polarity of the toner, which is the charge polarity of the toner during development, is negative polarity.

[0018] An intermediate transfer unit 44 is positioned opposite four photosensitive drums 51y, 51m, 51c, and 51k. The intermediate transfer unit 44 has an intermediate transfer belt 44b, which is an endless belt serving as a second image carrier. The intermediate transfer belt 44b is wrapped around several rollers, including a drive roller 44a, a driven roller 44d, primary transfer rollers 47y, 47m, 47c, 47k, and a secondary transfer inner roller 45a. The intermediate transfer belt 44b is movable (rotatable) and carries the toner image. The drive roller 44a is rotationally driven by a motor (not shown) as a driving means, causing the intermediate transfer belt 44b to rotate (circumferentially move). The driven roller 44d is a tension roller that controls the tension of the intermediate transfer belt 44b to be constant. The driven roller 44d is subjected to a force that pushes the intermediate transfer belt 44b toward its outer surface by the biasing force of a spring (not shown) as a biasing means, and this force applies a tension of about 2 to 5 kg to the intermediate transfer belt 44b in the process direction. The secondary transfer inner roller 45a constitutes the secondary transfer apparatus 45 as described later. The intermediate transfer belt 44b is driven by a driving force transmitted by the drive roller 44a and rotated in the direction of the arrow in the figure (clockwise) at a predetermined peripheral speed corresponding to the peripheral speed of the photosensitive drum 51. The intermediate transfer unit 44 also has a belt cleaning device 60 as an intermediate transfer body cleaning means.

[0019] The primary transfer rollers 47y, 47m, 47c, and 47k, which are roller-type primary transfer members serving as primary transfer means, are positioned opposite the photosensitive drums 51y, 51m, 51c, and 51k, respectively. The primary transfer roller 47 clamps the intermediate transfer belt 44b between itself and the photosensitive drum 51. As a result, the intermediate transfer belt 44b comes into contact with the photosensitive drum 51, forming a primary transfer portion (primary transfer nip portion) 48 between itself and the photosensitive drum 51.

[0020] The toner image formed on the photosensitive drum 51 is first transferred onto the intermediate transfer belt 44b in the primary transfer section 48 by the action of the primary transfer roller 47. In other words, in this embodiment, by applying a positive primary transfer voltage to the primary transfer roller 47, the negatively polarized toner image on the photosensitive drum 51 is first transferred onto the intermediate transfer belt 44b. For example, when forming a full-color image, the toner images of yellow, magenta, cyan, and black formed on each of the photosensitive drums 51y, 51m, 51c, and 51k are sequentially superimposed onto the intermediate transfer belt 44b in a multiple transfer process. A primary transfer power supply 75 (Figure 2) is connected to the primary transfer roller 47. During the primary transfer process, the primary transfer power supply 75 applies a DC voltage to the primary transfer roller 47 as a primary transfer bias (primary transfer voltage) that is the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner. The primary transfer power supply 75 is connected to a voltage detection sensor 75a for detecting the output voltage and a current detection sensor 75b for detecting the output current (Figure 2). In this embodiment, primary transfer power supplies 75y, 75m, 75c, and 75k are provided for each of the primary transfer rollers 47y, 47m, 47c, and 47k, and the primary transfer voltage applied to the primary transfer rollers 47y, 47m, 47c, and 47k can be controlled individually.

[0021] In this embodiment, the primary transfer roller 47 has an elastic layer of ion-conductive foamed rubber (NBR rubber) and a core metal. The outer diameter of the primary transfer roller 47 is, for example, 15 to 20 mm. Furthermore, the primary transfer roller 47 has an electrical resistance value of 1 × 10⁻⁶. 5 ~1 × 10 8 A roller with a value of Ω (N / N (measured at 23°C, 50%RH, with 2kV applied)) can be suitably used.

[0022] In this embodiment, the intermediate transfer belt 44b is an endless belt having a two-layer structure consisting of a base layer and a surface layer from the inner circumferential surface side. Suitable materials for the base layer include resins such as polyimide and polycarbonate, or various types of rubber containing an appropriate amount of carbon black as an antistatic agent. The thickness of the base layer is, for example, 0.05 to 0.15 mm. Suitable materials for the surface layer include resins such as fluororesin. The surface layer reduces the adhesion of toner to the surface of the intermediate transfer belt 44b, facilitating the transfer of toner to the recording material S in the secondary transfer section 45n. The thickness of the surface layer is, for example, 0.0002 to 0.020 mm. In this embodiment, the surface layer uses, for example, one type of resin material such as polyurethane, polyester, or epoxy resin, or two or more types of elastic materials such as elastic rubber, elastomer, or butyl rubber as the base material. Then, a surface layer is formed on this substrate by dispersing one or more types of powders or particles, such as fluororesin, or particles with different particle sizes, as a material that reduces surface energy and enhances lubricity. In this embodiment, the intermediate transfer belt 44b has a volume resistivity of 5 × 10⁻⁶ 8 ~1 × 10 14 The coefficient of static friction is [Ω·cm] (23℃, 50%RH) and 0.15~0.6 (23℃, 50%RH, HEIDON type94i). In this example, a two-layer structure was used, but a single-layer structure of the material corresponding to the above base layer may also be used.

[0023] On the outer circumferential surface of the intermediate transfer belt 44b, a secondary transfer outer roller 45b is arranged, which together with the secondary transfer inner roller 45a constitutes the secondary transfer device 45. The secondary transfer outer roller 45b contacts the intermediate transfer belt 44b, forming a secondary transfer section (secondary transfer nip section) 45n between itself and the intermediate transfer belt 44b. The secondary transfer outer roller 45b contacts the secondary transfer inner roller 45a via the intermediate transfer belt 44b. The toner image formed on the intermediate transfer belt 44b is secondarily transferred onto the recording material S in the secondary transfer section 45n by the action of the secondary transfer device 45. In this embodiment, by applying a positive polarity secondary transfer voltage to the secondary transfer outer roller 45b, the negative polarity toner image on the intermediate transfer belt 44b is secondarily transferred onto the recording material S, which is held and transported between the intermediate transfer belt 44b and the secondary transfer outer roller 45b. The recording material S is fed from a feeding unit (not shown) in parallel with the toner image formation operation described above, and is transported to the secondary transfer unit 45n by a register roller 11 provided in the transport path, with the timing synchronized with the toner image on the intermediate transfer belt 44b.

[0024] Thus, the secondary transfer device 45 is configured to include a secondary transfer inner roller 45a as an opposing member and a secondary transfer outer roller 45b, which is a roller-type secondary transfer member as a secondary transfer means. The secondary transfer inner roller 45a is positioned opposite the secondary transfer outer roller 45b via an intermediate transfer belt 44b. A secondary transfer power supply 76 (Figure 2) is connected to the secondary transfer outer roller 45b as an application means. During the secondary transfer process, the secondary transfer power supply 76 applies a DC voltage to the secondary transfer outer roller 45b as a secondary transfer bias (secondary transfer voltage) that is the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner. A voltage detection sensor 76a for detecting the output voltage and a current detection sensor 76b for detecting the output current are connected to the secondary transfer power supply 76 (Figure 2). The core metal of the secondary transfer inner roller 45a is connected to ground potential. Then, when the recording material S is supplied to the secondary transfer section 45n, a constant voltage controlled secondary transfer voltage with the opposite polarity to the normal charging polarity of the toner is applied to the secondary transfer outer roller 45b. In this embodiment, for example, a secondary transfer voltage of 1 to 6.5 kV is applied, and a current of about 15 to 100 μA flows, so that the toner image on the intermediate transfer belt 44b is secondary transferred onto the recording material S. In this embodiment, the secondary transfer inner roller 45a is connected to ground potential, and a voltage is applied to the secondary transfer outer roller 45b from the secondary transfer power supply 76. Alternatively, a voltage may be applied to the secondary transfer inner roller 45a, which is a secondary transfer member, from the secondary transfer power supply 76, and the secondary transfer outer roller 45b, which is an opposing member, may be connected to ground potential. In this case, a DC voltage with the same polarity as the normal charging polarity of the toner is applied to the secondary transfer inner roller 45a.

[0025] In this embodiment, the secondary transfer outer roller 45b has an elastic layer of ion-conductive foamed rubber (NBR rubber) and a core metal. The outer diameter of the secondary transfer outer roller 45b is, for example, 20 to 25 mm. Furthermore, the electrical resistance value of the secondary transfer outer roller 45b is 1 × 10⁻¹⁰. 5 ~1 × 10 8 A roller with a value of Ω (N / N (measured at 23°C, 50%RH, with 2kV applied)) can be suitably used.

[0026] The recording material S onto which the toner image has been transferred is transported to a fixing unit 46, which serves as a fixing means. The fixing unit 46 includes a fixing roller 46a and a pressure roller 46b. The fixing roller 46a has a built-in heater as a heating means. The recording material S, which carries the unfixed toner image, is heated and pressurized by being transported while sandwiched between the fixing roller 46a and the pressure roller 46b. As a result, the toner image is fixed (melted and solidified) onto the recording material S. The temperature of the fixing roller 46a (fixing temperature) is detected by a fixing temperature sensor 77 (Figure 2).

[0027] If the image is formed on one side of the recording material S, the recording material S is discharged directly to the paper discharge section 7. On the other hand, if the image is formed on both sides of the recording material S, the recording material S is transported to the inversion transport path 6. In the inversion transport path 7, the recording material S, on which the toner image has been fixed on the first side, is turned over and supplied again to the secondary transfer section 45n. After the recording material S is supplied again to the secondary transfer section 45n by the operation of the inversion transport path 6, the toner image is transferred to the second side and fixed, and then discharged from the paper discharge section 7. In this way, the image forming apparatus 2 of this embodiment is capable of performing automatic double-sided printing, in which an image is formed on both sides of a single sheet of recording material S.

[0028] After the primary transfer, the photosensitive drum 51 is electrostatically discharged from its surface by the pre-exposure device 54. Toner remaining on the photosensitive drum 51 during the primary transfer process (primary transfer residue toner) that was not transferred to the intermediate transfer belt 44b is removed from the surface of the photosensitive drum 51 by the cleaning blade 55 and collected in a collection container (not shown). The cleaning blade 55 is a plate-shaped member that contacts the photosensitive drum 51 with a predetermined pressing force. The cleaning blade 55 is in contact with the surface of the photosensitive drum 51 in a counter-direction, with its free end facing upstream in the rotational direction of the photosensitive drum 51. Furthermore, toner remaining on the intermediate transfer belt 44b during the secondary transfer process (secondary transfer residue toner) and other adhering materials such as paper dust are removed from the surface of the intermediate transfer belt 44b by the belt cleaning device 60 and collected.

[0029] An automatic document transport device 81 and an image reading unit 80 are located at the top of the main body 10 of the image forming apparatus. The image reading unit 80 optically reads the image on the document set on the platen glass 82, or on the document transported onto the platen glass 82 by the automatic document transport device 81, and converts it into an electrical signal.

[0030] Figure 2 is a block diagram illustrating the schematic configuration of the control system of the image forming apparatus 2 in this embodiment. As shown in Figure 2, the control unit 30 is composed of a computer and includes, for example, a CPU 31, a ROM 32 that stores programs for controlling each part, a RAM 33 that temporarily stores data, an input / output circuit (I / F) 34 that inputs and outputs signals to and from the outside, and an HDD 35 that stores data. The CPU 31 is a microprocessor that oversees the entire control of the image forming apparatus 2 and is the main component of the system controller, operating based on the program stored in the RAM 33. The CPU 31 is connected to the feed unit 4, the image forming unit 5, and the operation unit 70 via the input / output circuit 34, and exchanges signals with each of these parts and controls the operation of each of these parts. The ROM 32 is a boot ROM and stores the system's boot program. The control unit 30 is connected to a charge bias power supply 73, a development bias power supply 74, a primary transfer power supply 75, and a secondary transfer power supply 76, each of which is controlled by signals from the control unit 30. Furthermore, the control unit 30 is connected to a temperature sensor 71, a humidity sensor 72, a voltage detection sensor 75a and a current detection sensor 75b of the primary transfer power supply 75, a voltage detection sensor 76a and a current detection sensor 76b of the secondary transfer power supply 76, and a fixing temperature sensor 77. Signals detected by each sensor are input to the control unit 30. The HDD 35 stores system software, image data, and programs for controlling the operation of the image forming apparatus 2. The programs stored in the HDD 35 are loaded into the RAM 33, and the CPU 31 controls the operation of the image forming apparatus 2 based on these programs.

[0031] The operation unit 70 includes operation buttons as input means and a display unit 70a consisting of a liquid crystal panel or the like as a display means. In this embodiment, the display unit 70a is configured as a touch panel and also functions as an input means. Operators such as users and service personnel can execute a job (a series of operations that form and output an image on one or more recording materials S with a single start command) by operating the operation unit 70. The control unit 30 receives signals from the operation unit 70 and operates various devices of the image forming apparatus 2. The image forming apparatus 2 can also execute jobs based on image forming signals (image data, control commands) from external devices 200 such as a personal computer.

[0032] In this embodiment, the control unit 30 includes an image formation preparation process unit 31a, an ATVC control process unit 31b, an image formation process unit 31c, and an adjustment process unit 31d. The control unit 30 also includes a primary transfer voltage storage / calculation unit 31e and a secondary transfer voltage storage / calculation unit 31f. These process units and storage / calculation units may be provided as part of the CPU 31 or RAM 33. For example, the control unit 30 (more specifically the image formation process unit 31c) can execute jobs as described above. The control unit 30 (more specifically the adjustment process unit 31d) can also execute an adjustment mode to adjust the setting voltage of the secondary transfer voltage when not forming an image. The adjustment mode will be described in detail later. Here, the image forming apparatus 2 performs a "job," which is a series of image output operations that form and output an image on one or more recording materials M, initiated by a start instruction from the control unit 30. A job generally consists of an image formation process (printing process), a pre-rotation process, a paper-to-paper process when forming an image on multiple recording materials M, and a post-rotation process. The image formation process is the period during which the electrostatic latent image of the image to be actually formed and output on the recording material M is formed, the toner image is formed, the toner image is transferred, and the toner image and recording material are fixed. The term "image formation time" refers to this period. The pre-rotation process is the period from when the start instruction is input until the image is actually formed, during which preparatory operations are performed before the image formation process. The paper-to-paper process is the period corresponding to the space between recording materials M when performing continuous image formation, where images are formed on multiple recording materials M in succession. The post-rotation process is the period during which cleanup operations (preparatory operations) are performed after the image formation process. Non-image formation time refers to periods other than the image formation time, and includes the pre-rotation process, paper-to-paper process, post-rotation process, and preparatory operations such as the pre-multi-rotation process when the image forming apparatus 2 is powered on or when it returns from sleep mode.

[0033] Figure 3 is a side cross-sectional view showing the internal structure of the scanner unit. The automatic document transport device 81 has a document tray 300 for loading documents to be scanned, and a document sensor 302 for detecting the presence or absence of documents, two document guides 301, and a document size detection sensor 303 are provided on the document tray 300. Two document guides 301 are provided side by side in the vertical direction of the document (perpendicular to the document transport direction), and documents loaded on the document tray 300 are transported by three rollers: a pickup roller 304, a transport roller 306, and a paper output roller 309. The pickup roller 304 is a roller for transporting documents loaded on the document tray 300 into the document transport path inside the ADF unit. The transport roller 306 transports documents that have been transported into the document transport path by the pickup roller 304, and the paper output roller 309 transports documents that have been transported by the transport roller 306 to the paper output tray 310. Furthermore, the document transported by the pickup roller 304 is detected by the document passage detection sensor 305, and it is determined whether the first document has finished passing based on the detection time. Although not shown in the diagram, the transport roller 306, pickup roller 304, and paper discharge roller 309 are all driven by stepping motors. The sub-scanning decimation process in the automatic document transport device 81 is achieved by doubling the frequency of the drive pulses of the transport, pickup, and paper discharge rollers. The transported document is read by the CIS 308 provided in the sensor unit 311 located below the reading window 307. The sensor unit 311 can move freely in the sub-scanning direction and can also move in the same direction as the transport direction of the document being transported from the transport roller 306 towards the paper discharge roller 309. The reading window 307 has a certain length in the sub-scanning direction, and within that length, the CIS 308 can be moved to any position and the document can be read at that position. The CIS308 is composed of photoelectric conversion elements such as a CCD, and simultaneously generates a FIFO for accumulating images from each element, as well as control signals for controlling the FIFO and the CCD. The CIS308 is generally implemented by arranging multiple photoelectric conversion elements in a line.Although not shown in the diagram, the sensor unit 311 is also equipped with a light source for illuminating the document through the reading window 307 or the document glass reading window 312, and is generally implemented by arranging multiple light sources in a line. An example of a light source is an LED, but other types of light sources may also be used. The aforementioned platen glass 82 refers to the reading window 307 and the document glass reading window 312 combined.

[0034] If the user places a document on the document glass instead of the document tray 300, the sensor unit 311 is moved below the document glass reading window 312, and the document is read by the CIS 308 through the document glass reading window 312 while the sensor unit 311 is moved in the sub-scanning direction. The read image data is saved in the RAM 33 or in an image memory dedicated to image data storage (not shown).

[0035] Figure 4 shows an example of a pattern image used for adjusting the secondary transfer voltage output in this embodiment. This pattern image 400 is stored in the HDD 35 and read into the RAM 33 to form an image on the recording material S based on this image, and a test chart for adjusting the secondary transfer voltage is output. Alternatively, the CPU 31 may be configured to form this pattern on the RAM 33 and output the test chart. The patch pattern and band pattern in Figure 4 are of the same density and dithering type for those arranged vertically. Pattern image 400 includes band patterns 401 and 402 as test images for adjusting the secondary transfer voltage. It also includes patch patterns 403 and 404 as test images for adjusting the secondary transfer voltage. Furthermore, pattern image 400 is configured to include a secondary transfer voltage value display 405, a black band 406 for determining the reference position as a reference image, and a page identification patch 407 as a page identification image. Band patterns 401 and 402 are black halftone images. Patch pattern 403 consists of a solid black density, and 404 consists of a solid blue density (a solid density created by superimposing two solid color images). The secondary transfer voltage value display 405 displays the secondary transfer voltage value applied when forming the patch, and is a display that the user can refer to when making visual adjustments. The black band 406 for determining the reference position consists of a solid black density. That is, it is formed from an image with a higher density than band patterns 401 and 402. The page identification patch 407 consists of a solid CMYK single color density. When adjusting the image reading unit 80 when outputting a chart on multiple pages, such as in double-sided printing, the page identification patch 407 is analyzed to determine which page was read. The page identification patch 407 may be a mixture of CMYK colors instead of a single color. The pattern image 400 may include a pattern indicating the page number that corresponds to the color of the page identification patch 407, although this is not shown in the illustration.

[0036] When forming the above patterns on the recording material S, the secondary transfer voltage applied to each vertical band pattern and patch pattern in Figure 4 is varied. This makes it possible to visually or with a reading device determine which voltage value is optimal for printing from the output chart. To simplify control, the secondary transfer voltage applied when forming the black band 406 for reference position determination and the patch 407 for page identification is set as follows: It is the same as the secondary transfer voltage applied when forming the bottommost band patterns 401, 402, and patch patterns 403, 404 in Figure 4. However, for the black band 406 for reference position determination and the patch 407 for page identification, it is also possible to apply a secondary transfer voltage of a specific value determined based on the type of recording material on which the pattern is formed.

[0037] The user can visually inspect the pattern formed on the recording material S and determine the optimal secondary transfer voltage value by referring to the secondary transfer voltage value display 405 and each patch pattern and band pattern, and then set it from the operation unit 70. Alternatively, the pattern formed on the recording material S can be read by the image reading unit 80, and the optimal secondary transfer voltage value can be determined by analyzing the read image stored in the RAM 33 with the CPU 31 (the adjustment mode described above). Details of the adjustment using the image reading unit 80 will be described later, but the optimal secondary transfer voltage value is determined based on the brightness value of at least one of the band patterns 401, 402 and patch patterns 403, 404. The adjustment value of the secondary transfer voltage can be set differently on the front and back of the paper, and it is also possible to adjust both sides on a single sheet of paper by forming pattern images 400 on both sides of the recording material S and performing the adjustment.

[0038] Image pattern 400 is used for both visual correction and correction using the image reading unit 80. Furthermore, when visually correcting the secondary transfer voltage, it is desirable to primarily refer to the printing state of the solid-density patch patterns 403 and 404. Pattern image 400 is designed for use on recording media of a certain size or larger in both width and length, such as A3 paper. However, the narrower the paper width, the fewer patterns can be formed on the paper. Therefore, the priority patch patterns 403 and 404 are placed closer to the horizontal center of the image, while the band patterns 401 and 402 are placed at the edges of the image. When using narrower paper, the width of the printed band patterns 401 and 402 becomes shorter, and they may not be formed on paper of a width equivalent to A5R. Correction using the image reading unit 80 targets paper of a certain size or larger so that the band patterns 401 and 402 are formed on the recording media.

[0039] Figure 5(a) is a top view of a chart with a pattern image 400 formed on the recording material S, set on the document scanning window 312 with the printed side facing downwards. In this figure, the chart is set so that the upper left corner abuts against the chart, which is the most appropriate setting method assumed.

[0040] Figure 5(b) shows an image obtained by reading the chart with the chart positioned as shown in Figure 5(a) using the document reading unit 80. The reading size of the document may be determined by storing the size of the chart's printing paper in RAM 33 and reading an area of ​​the same size with the document reading unit 80. Alternatively, a fixed area larger than the size of the printing paper may be defined and read. In this embodiment, the former example is shown.

[0041] In this state, there are no problems with edge detection of band patterns and patch patterns.

[0042] Figure 6(a) is a top view of a chart with a pattern image 400 formed on the recording material S, set on the document reading window 312 with the printed side facing down. In this figure, the chart is not aligned with the upper left stopper, but is set further back towards the sub-scan end of the document reading unit 80 than in Figure 5(a). This is intended to account for cases where the user sets the document carelessly or is unaware that it should be set with the upper left stopper.

[0043] Figure 6(b) shows the image obtained by reading the chart with the chart positioned as shown in Figure 6(a) using the document reading unit 80. Because there is a gap between the chart and the leading edge of the sub-scanning area, the white plate (not shown) that holds the document on the document glass reading window 312 is read. Therefore, the reading of the white plate is added to the top of the resulting image.

[0044] In this state, there are no problems with edge detection of band patterns and patch patterns.

[0045] Figure 7(a) shows an example of edge detection performed on the read image in Figure 6(b) to determine the position of band patterns 401 and 402. Brightness values ​​are checked from the top edge of the image downwards, and positions where the change in brightness value between adjacent pixels exceeds a certain level are determined as pattern edges. Although not shown, edge detection may also be performed on patch patterns 403 and 404. The vertical center coordinates of each band pattern or patch pattern are determined from the edges detected by vertical scanning, and similarly, edge detection is performed on the horizontal direction of the image based on the change in brightness between adjacent pixels using these coordinates. The position of the pattern is identified from the top, bottom, left, and right edges of the band and patch patterns obtained in this way, and the positions for sampling brightness values ​​for adjustment are determined.

[0046] The threshold for determining an edge based on luminance difference is set so that the thinnest pattern constituting band patterns 401 and 402, and patch patterns 403 and 404 can be detected. Furthermore, the threshold for determining an edge based on luminance difference is set so that detection is possible even when images are formed with secondary transfer voltages that are not necessarily optimal for various assumed papers used for correction. In particular, as mentioned above, it is desirable to be able to reliably detect band patterns 401 and 402, which are close to the left and right edges of the image, in order to accurately determine the image angle. As a result, the threshold becomes a relatively lenient condition that can be easily satisfied. At least one of the luminance RGB components that make up the pixels of the read image is used as a condition. The condition may be set using other color representation methods besides RGB.

[0047] When performing edge detection in the horizontal direction, it is necessary to consider the tilt of the original document, so the calculation is performed using the coordinates of the detected edges or the vertical center coordinates obtained from the upper and lower edges of each patch as described above. To determine the angle more accurately, it is preferable to use the coordinates obtained from band patterns 401 and 402, which are as far apart as possible in the horizontal direction of the image, rather than the coordinates obtained from patch patterns 403 and 404.

[0048] Figure 7(b) shows an example of edge detection performed on an image obtained using colored paper, similar to Figure 7(a), to determine the positions of band patterns 401 and 402. Because colored paper is used, there is a difference in brightness at the boundary between the white plate scanned at the top of the image and the original document. As mentioned above, judging based on a loose threshold will result in a misidentification of an edge. This leads to the detection of one extra vertical edge, which makes it impossible to determine the position of each pattern.

[0049] Figure 8 illustrates the solution to the above problem using the procedure of this implementation. The procedure for edge detection of band patterns 401 and 402 and patch patterns 403 and 404 is divided into three parts.

[0050] Figure 8(a) shows the first step in detecting the edges of the black bar 406 used for determining the reference position. Edge detection is performed by detecting the change in brightness between adjacent pixels, starting from the bottom edge of the read image and moving upwards. If two edges are found on each scan line, the scan is terminated, and the vertical center coordinates of the black bar used for determining the reference position are determined from the upper and lower edge detection positions on each scan line. The tilt of the black bar 406, i.e., the tilt of the entire image, is determined from the two points obtained by scanning the two lines obtained, and if the tilt is greater than a certain level, it is determined that a different location was misdetected instead of the black bar 406. In other words, in this embodiment, the black bar 406 used for determining the reference position also serves as a tilt detection image for detecting the tilt of the entire image. Next, if it is determined that the black bar 406 has been detected, an area a certain distance away from the detection position of the black bar 406 is scanned to detect the page identification patch 407, and if detected, the process proceeds to the next step. The detection of identification patch 407 begins by classifying and voting on which of the possible colors for page identification patch 407 it is closest to, based on RGB conditions, using the color information of each pixel in the scanned area. Then, if a certain number of votes for a particular color are found to be above a certain threshold, it is determined to be the patch of the color that received the most votes. Other image analysis methods, such as pattern matching, may also be used for patch detection.

[0051] Furthermore, the threshold for luminance difference used to determine the edge of the black band 406 for determining the reference position (the threshold for luminance difference) is set to a condition that is at least stricter than the threshold for determining the edges of the band patterns 401, 402, and the patch patterns 403, 404. Specifically, the assumed luminance values ​​for each of the following (1) to (4) when read by the document reading unit 80 are determined in advance. The assumed luminance values ​​for each of these are determined in advance: (1) the white plate of the document reading unit 80, (2) the most colored paper that is allowed, (3) the lightest pattern among the band patterns 401, 402 or the patch patterns 403, 404 of the chart, and (4) the black band 406 for determining the reference position. By increasing the density of the black band 406 for determining the reference position, (4)-(2) can be detected as edges, but the edge detection threshold can be set so that (2)-(1) are not detected as edges. The reason this embodiment is necessary is that while (3)-(2) can be detected as an edge, it is difficult to determine the threshold for determining the edges of band patterns 401, 402 and patch patterns 403, 404 so as not to detect (2)-(1) as an edge.

[0052] Figure 8(b) shows the second step in determining the vertical position to start edge detection for band patterns 401, 402 and patch patterns 403, 404. The vertical coordinates are set so that they fall within the chart area, by moving a fixed number of pixels upward from the vertical center coordinate of the black band 406 used for determining the reference position, which was determined in the previous step. Specifically, the size of the printed recording material S of the chart is stored in RAM 33, and the upper edge of the chart area can be determined by subtracting the sub-scan length of the recording material S from (the distance from the bottom edge of the image in the pattern image 400 to the center of the black band 406 used for determining the reference position). However, if edge searching is performed from the upper edge of the chart area, there is a possibility that the boundary between the part where the white plate was read and the part where the chart was read may be scanned due to errors, so it is desirable to offset by a fixed amount and set the scanning start position to the area inside the chart.

[0053] Figure 8(c) shows the third step in which edge detection is performed on band patterns 401 and 402 and patch patterns 403 and 404. Edge detection is performed by detecting changes in brightness between adjacent pixels, starting from the vertical position of the image defined in the previous step and moving downwards. Since scanning starts from within the chart area of ​​the read image, the edges of the patterns can be detected without misdetecting the boundary between the white plate read portion and the chart read portion.

[0054] Figure 9(a) is a top view of a chart with a pattern image 400 formed on the recording material S, rotated 180 degrees relative to Figure 6(a), and set on the document scanning window 312. From a usability standpoint, it is preferable that adjustments can be made appropriately even in such cases, so that the user does not have to consider the orientation in which to set the document. The operation when the document is set in such an orientation in Example 1 will be explained.

[0055] Figure 9(b) shows an image obtained by reading the chart using the document reading unit 80 with the chart positioned as shown in Figure 9(a). Compared to Figure 6(b), the chart area of ​​the read image is rotated 180 degrees, and the area where the white plate was read is added to the top of the image.

[0056] Figure 10 is a diagram illustrating the operation in Example 1 with respect to the image in Figure 9(b).

[0057] Figure 10(a) shows a case where patch patterns 403 and 404 are mistakenly detected as the black band 406 used for determining the reference position during edge detection. In this case, the position of the black band 406 used for determining the reference position is incorrectly detected, but as mentioned above, if detection of the page identification patch 407 is performed based on that position, detection fails because there is no pattern. In this case, it is determined that the document is set up 180 degrees in the wrong direction, and the entire scanned image is rotated 180 degrees and the edge detection of the black band 406 used for determining the reference position is attempted again.

[0058] Figure 10(b) shows a case where no edge was detected during edge detection of the black band 406 used for determining the reference position. This occurs when the main scanning position where the chart is set on the document glass is shifted, as the horizontal positions of the two lines scanning the black band 406 used for determining the reference position are fixed. If edge detection of the black band 406 used for determining the reference position is attempted for a certain number of pixels and no two edges are detected on each scanning line, it is determined that the document is set in the wrong direction (180 degrees reversed), and the entire scanned image is rotated 180 degrees and edge detection of the black band 406 used for determining the reference position is attempted again.

[0059] Figure 10(c) shows an example where the black bar 406 for determining the reference position could not be detected correctly as described above, and the image was rotated 180 degrees before attempting to detect the edge of the black bar 406 again. Regarding the edge detection of the black bar 406 for determining the reference position, even if scanning starts from the lower edge of the image where the white plate was read, a strict threshold is set to prevent the boundary between the white plate and the chart area from being mistakenly identified as an edge, as mentioned above. This ensures that the edge detection of the black bar 406 for determining the reference position can be performed appropriately.

[0060] Figure 11 is a flowchart of the adjustment process for reading the secondary transfer voltage chart in the control unit 30 in the embodiment. The program executed by the CPU 31 related to this flowchart is stored in the ROM 32 and loaded into the RAM 33.

[0061] This flowchart assumes that the chart formed on the recording material S is read by the image reading unit 80 and the obtained image is stored in the RAM 33 when the flowchart starts, and the CPU 31 executes each step.

[0062] In S1101, as shown in Figure 8(a), the image is scanned upwards from the bottom edge. If a point is found where the brightness difference between adjacent pixels exceeds a certain level, it is determined to be an edge of the black band 406 used for determining the reference position. If the page identification patch 407 cannot be detected based on edge detection, or if two edges cannot be detected even after scanning a certain distance, the scan is terminated. The scan is performed on two lines. Proceed to S1102.

[0063] In S1102, if two edges were detected on both lines in S1101, and the tilt of the black band 406 for determining the reference position was below the reference value as described above, it is determined that the black band 406 for determining the reference position was detected, and the process proceeds to S1106. If it could not be detected, the process proceeds to S1103.

[0064] In S1103, it is determined by S1104 whether the scanned image has already been rotated 180 degrees. If it has not been rotated, proceed to S1104. If it has been rotated, proceed to S1105.

[0065] In S1104, the scanned image is rotated 180 degrees. This 180-degree rotation can be performed by the CPU 31, or by an image processing ASIC (not shown in the diagram). Alternatively, a flag may be set to perform subsequent scans in the reverse direction without actually rotating the image. Proceed to S1101.

[0066] In S1105, an error occurs because the scanned image is unsuitable for adjustment, and this is displayed on the display unit 70a. The error screen prompts the user to check whether the adjustment chart is set in the document scanning unit 80 and whether the document orientation is correct. The system may then proceed to a screen where the user can instruct the system to scan the document. The flow ends without updating the adjustment values.

[0067] As mentioned above, S1106 detects the position of the page identification patch 407 based on the detection position of the black band 406 used for determining the reference position. It then determines which page identification patch 407's color is closest to the pixel in a specific area.

[0068] S1107 determines whether page identification patch 407 was detected. If detected, proceed to S1108. If not detected, proceed to S1103.

[0069] In S1108, as shown in Figure 8(b), the scanning start position for detecting the edges of the adjustment pattern is determined based on the position of the black band 406 used for determining the reference position. Proceed to S1109.

[0070] In S1109, as shown in Figure 8(c), edge detection is performed on band patterns 401 and 402 and patch patterns 403 and 404, starting from the position determined in S1108 and moving downwards from the image. The number of lines and positions to be scanned are set so that at least one line each of band patterns 401 and 402 is passed through. If possible, increasing the number of lines to be scanned allows for adjustment using edge detection results from other lines if an edge could not be detected on a line with a sudden image defect. The subsequent lateral edge scanning of the image is as described above, so the explanation will be omitted. Proceed to S1110.

[0071] In S1110, it is determined whether band patterns 401 and 402 and patch patterns 403 and 404 have been detected. The determination of whether band patterns 401 and 402 and patch patterns 403 and 404 have been detected is made in the following two ways: First, it is determined by whether all the edges that should be detected on two lines that are separated by a certain distance have been detected in the vertical edge detection scan by S1109. Second, it is determined by whether all the edges that should be detected for all band patterns 401 and 402 and patch patterns 403 and 404 have been detected in the subsequent horizontal edge scan. If in both cases the edges have been detected, it is determined that the adjustment patterns have been detected and the process proceeds to S1111. If the number of detected edges is insufficient, the process proceeds to S1105. It may also be configured so that even if the expected number of edges are detected, if the detection interval is not constant, it is treated as an error and the process proceeds to S1105.

[0072] In S1111, the positions of each band pattern 401, 402, and patch patterns 403, 404 are identified from the edge detection positions in the vertical and horizontal directions detected in S1110, and the brightness values ​​of specific areas, such as near the center of the pattern, are obtained. Proceed to S1112.

[0073] In S1112, the adjustment value for the secondary transfer voltage is calculated using the brightness value obtained in S1111, and the adjustment values ​​stored in RAM33 and HDD35 are updated. The calculation process for the adjustment value is a well-known technique and is therefore not described here. Proceed to S1113.

[0074] In S1113, the display unit 70a displays that the adjustment has been successfully completed, and the adjustment flow is terminated. Alternatively, the adjustment value obtained in S1112 may be displayed on the display unit 70a, allowing the user to confirm the value and make fine adjustments.

[0075] By following the above procedure, even when using colored paper and having to set a loose detection threshold for the adjustment pattern, the adjustment can be performed by appropriately detecting and sampling the adjustment pattern. Although this embodiment describes its application to the adjustment of the secondary transfer voltage, it can be similarly applied to adjustment functions that print and read charts, which are expected to be used with various types of paper.

[0076] Furthermore, although this embodiment describes the reading device as reading a test chart set on a document glass, it may also be configured to read a test chart output using an inline sensor. [Explanation of Symbols]

[0077] 51 Photosensitive drum 400 pattern images 406 Black bar for determining reference position (reference image) Page 407 Identification Patch (Identification Image)

Claims

1. an image carrier that carries a toner image; a transfer member forming a transfer section that transfers a toner image from the image carrier to a recording material; a power source that applies a transfer voltage to the transfer member; a control unit that applies a plurality of different voltages to the transfer member by the power source during non-image formation, transfers a plurality of test images from the image carrier to a recording material, and outputs a test chart for adjusting the transfer voltage to be set during image formation; a reading device for reading the test chart; and an image forming apparatus capable of adjusting the transfer voltage set during image formation based on a reading result of the reading device, an image forming apparatus characterized in that the control unit is configured to form a reference image on a recording material on which the test chart is formed to determine the start position for reading the test image by the reading device, and the reading device is configured to determine the start position for reading the test image based on the position of the reference image when the reference image is detected.

2. 2. The image forming apparatus according to claim 1, wherein the control unit determines the reading start position of the test image based on the detection result of the reference image by the reading device so that the reading start position of the test image is within the frame of the recording material on which the test chart is formed.

3. 3. The image forming apparatus according to claim 1, wherein the plurality of test images include at least halftone images, and the reference image has a higher density than the halftone images.

4. The image forming apparatus of any one of claims 1 to 3, characterized in that the reading device is configured to read the reference image based on a first threshold value regarding the luminance difference between adjacent pixels and to read the test image based on a second threshold value regarding the luminance difference between adjacent pixels, and the first threshold value is larger than the second threshold value regarding the luminance difference.

5. 5. The image forming apparatus according to claim 1, wherein the control unit is configured to read the test chart in a reverse direction when it is determined that the reference image cannot be read.

6. 6. The image forming apparatus according to claim 1, wherein the reference image also serves as an image for detecting tilt of the test image.

7. 7. The image forming apparatus according to claim 1, wherein the reference image is a solid black image.

8. 8. The image forming apparatus according to claim 1, wherein the control unit is configured to output an identification image for identifying the page number of the test chart, and is configured to determine a start position for reading the test image based on the reference image and the identification image.

9. 9. The image forming apparatus according to claim 1, further comprising a document table on which a recording material on which the test chart is formed is set, and the reading device is configured to read the test image on the recording material set on the document table.

Images