Image forming device

Abstract

To provide an image forming apparatus that can correct a writing position of an image with reduced toner consumption.SOLUTION: An image forming apparatus of the present embodiment has an image forming section having an optical unit and an image carrier, a developer adhesion amount sensor, and a control section. A laser optical unit forms a latent image through irradiation with light. The image carrier carries an image of developer. The image forming section forms the latent image formed on the image carrier by the laser optical unit as the image of developer. The developer adhesion amount sensor detects the amount of adhesion of developer in a pattern image formed by the image forming section for detecting the density of developer. The control section has control capable of correcting, based on a result of detection performed by the developer adhesion amount sensor, the timing at which the laser optical unit starts the irradiation or the timing at which a sheet to which the image of developer is transferred is conveyed based on a relative value from a predetermined detection start position to a predetermined reference position in the pattern image.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] An embodiment of the present invention relates to an image forming apparatus. [Background technology]

[0002] In electrophotographic MFPs (Multifunction Peripherals) that use toner for image formation, internal components can become deformed due to temperature rises caused by continuous printing, or changes in temperature and humidity depending on the installation location. This causes changes in the distance and position of the laser of the laser optical unit that irradiates the photosensitive drum, causing deviations in the leading edge position when writing the image. Therefore, it was necessary to correct the leading edge position of the image by forming and reading a special test pattern at a specified timing. However, extra toner was consumed every time this test pattern was formed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2000-47447 Summary of the Invention [Problem to be solved by the invention]

[0004] The problem to be solved by the present invention is to provide an image forming apparatus capable of correcting the writing start position of an image while suppressing toner consumption. [Means for solving the problem]

[0005] In order to solve the above problems, the image forming apparatus of the present embodiment includes an image forming section having an optical unit and an image carrier, a developer adhesion amount sensor, a transfer section, a registration roller, and a control section. The laser optical unit forms a latent image by irradiating light. The image carrier carries the developer image. and moves the developer image carried in a predetermined direction.The image forming unit converts the latent image formed on the image carrier by the laser optical unit into a developer image. On the image carrier Formed A plurality of developer images of different densities are successively formed in the predetermined direction. In the pattern image for detecting the concentration of the developer, the amount of developer adhered A value indicating the concentration of developer based on The transfer section transfers the developer image formed on the image carrier onto the paper. The registration roller conveys the paper to the transfer section at a predetermined timing. The control section detects the amount of developer adhesion detected by the developer adhesion sensor. a predetermined value set according to a density difference between a developer image of a predetermined density and a developer image successive to the developer image of the predetermined density in order to detect an edge of the developer image of the predetermined density in the pattern image; Based on a leading edge and a trailing edge of the developer image of the predetermined density in the predetermined direction are detected, and a central portion from the leading edge to the trailing edge is set as a reference position; From a given detection start position The above The control is capable of correcting the timing for transporting the paper onto which the developer image is transferred, based on a relative value to the reference position. [Brief description of the drawings]

[0006] [Figure 1] 1 is a schematic diagram illustrating a configuration of an image forming apparatus according to a first embodiment. [Diagram 2] 1 is a schematic diagram of a direct transfer type image forming unit in an image forming apparatus according to a first embodiment. [Diagram 3] 2 is a schematic diagram of a toner adhesion amount sensor in the image forming apparatus according to the first embodiment; FIG. [Figure 4] 1 is a block diagram illustrating the configuration of an image forming apparatus according to a first embodiment. [Diagram 5] 5A and 5B are diagrams illustrating a test pattern for density adjustment and an output waveform of a toner adhesion sensor according to the first embodiment. [Figure 6] 13A and 13B are diagrams illustrating a test pattern for density adjustment and an output waveform of a toner adhesion amount sensor according to a first modified example. [Figure 7] FIG. 4 is a flowchart illustrating image writing position correction control according to the image forming apparatus of the first embodiment. [Figure 8] 13 is a schematic diagram of an intermediate transfer type image forming unit in an image forming apparatus according to a second embodiment. FIG. [Figure 9] FIG. 11 is a schematic diagram of an intermediate transfer type image forming unit in an image forming apparatus having multi-color toners according to a second modified example. [Figure 10] 13A and 13B are diagrams illustrating a test pattern for density adjustment and an output waveform of a toner adhesion sensor according to a second modified example. [Figure 11] 13 is a flowchart showing color registration correction control in an image forming apparatus according to a second modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The image forming apparatus 10 according to the embodiment of the present invention can correct the image writing position on the paper based on the detection result of the toner adhesion amount sensor 61 that detects the image density used for the density adjustment control. The density adjustment control is a control for correcting the toner image formed on the toner image carrier to have an appropriate density.

[0008] Hereinafter, an embodiment of the invention will be described with reference to the drawings.

[0009] Fig. 1 is a schematic diagram showing an image forming apparatus 10. The image forming apparatus 10 of the first embodiment is a monochrome multifunction machine using an electrophotographic system. The image forming apparatus 10 shown in Fig. 1 includes an operation input unit 1, a reading unit 2, a paper storage unit 3, a conveying unit 4, and an image forming unit 5.

[0010] The operation input unit 1 accepts operation input from a user. The operation input unit 1 has physical keys and a display. The physical keys allow various operations to be input to the image forming apparatus 10 by pressing specific keys. The display displays specific information. The display may be configured as, for example, a touch panel display, and various operations can be input to the image forming apparatus 10 by touching the screen.

[0011] The reading unit 2 reads image information formed on a document to be read as light and dark, and records the image information in the memory 8. The recorded image information may be sent to an external device 91, or may be formed as an image on a sheet of paper by the image forming unit 5. The reading unit 2 may be an automatic document feeder such as an ADF (Auto Document Feeder) or a DSDF (Dual Scan Document Feeder) capable of simultaneously reading both sides of a sheet of paper, and is installed, for example, on the top of the image forming apparatus 10. The automatic document feeder transports the document to be read so that it passes through the automatic document feeder or a scanner provided in the image forming apparatus 10, and can read the image information.

[0012] The paper storage unit 3 stores paper for transferring an image. Paper used by the image forming apparatus 10 for transferring an image is fed from the paper storage unit 3 or a manual paper tray (not shown). The paper for transferring an image may be, for example, a film, and there is no limitation on the medium to which the image is transferred.

[0013] The conveying section 4 is a paper conveying path having multiple rollers that conveys paper onto which a toner image is transferred in the image forming apparatus 10 from the paper storage section 3 or a manual paper tray (not shown). The conveying section 4 has a registration roller 41 upstream of a fixing section 55 (described later) in the direction in which the paper is conveyed. The registration roller 41 temporarily stops the paper conveyed by the conveying section 4, and conveys the paper toward the transfer position at a predetermined timing so that the toner image formed on a carrier (toner image carrier) that carries the toner image and the paper come into contact at the transfer position 54. The timing at which the registration roller 41 resumes conveying the paper is controlled by the control section 7.

[0014] The image forming unit 5 develops the electrostatic latent image written on the photosensitive drum 51 into a toner image, and transfers it onto a sheet of paper.

[0015] The following describes the configuration of the image forming unit 5. Fig. 2 is a schematic diagram showing an example of the configuration of the image forming unit 5. The image forming unit 5 has a photosensitive drum 51, a laser optical unit 52, a developing device 53, a transfer unit 54, a fixing unit 55, and a cleaning blade 56.

[0016] The photosensitive drum 51 is a toner image carrier on whose surface a toner image is formed. The photosensitive drum 51 rotates in the direction of the arrow a during image formation. The surface of the photosensitive drum 51 is charged by a charger (not shown), and the irradiated portion is discharged by irradiating it with a laser beam from the laser optical unit 52. As a result, a latent image is formed on the surface of the photosensitive drum 51.

[0017] The laser optical unit 52 irradiates the photosensitive drum 51 with laser light for forming a latent image. A latent image is formed on the photosensitive drum 51 according to the intensity of the laser light irradiated from the laser light unit. The arrow extending from the laser optical unit 52 in FIG. 2 indicates the laser light.

[0018] The developing unit 53 develops the latent image held by the photosensitive drum 51 with toner of a specific color. The developing unit 53 has black toner, for example, in the first embodiment, and develops a black toner image on the photosensitive drum 51.

[0019] The transfer unit 54 transfers the toner image on the photosensitive drum 51 onto paper. The transfer unit 54 has a transfer roller 541. The transfer roller 541 is placed so as to come into contact with the photosensitive drum 51. The transfer roller 541 attracts the toner on the photosensitive drum 51 by being charged with a polarity opposite to that of the toner on the photosensitive drum 51. The transfer roller 541 can form a toner image on the paper by attracting the toner on the photosensitive drum 51 across the paper.

[0020] The fixing unit 55 fixes the toner image onto the paper by, for example, applying heat and pressure to melt the toner image formed on the paper and fixing it onto the paper.

[0021] The cleaning blade 56 is a member that scrapes off and removes waste toner remaining on the photosensitive drum 51 after transfer.

[0022] The sensor unit 6 generates various signals according to the operation of the image forming apparatus 10. The sensor unit 6 has a toner adhesion amount sensor 61. The toner adhesion amount sensor 61 is an optical sensor that detects the toner carried on the toner image carrier. The toner adhesion amount sensor 61 is installed downstream of the developing device 53 and upstream of the cleaning blade 56 in the moving direction of the toner image.

[0023] In addition, when the toner adhesion sensor 61 is used for measurement, the transfer roller 541 is controlled not to be charged with a charge of the opposite polarity to the toner on the photosensitive drum 51, so that the toner on the photosensitive drum 51 is not attracted to the transfer roller 541. However, since the photosensitive drum 51 and the transfer roller 541 are in contact with each other, the toner on the photosensitive drum 51 may adhere to the transfer roller 541, which may deteriorate the accuracy of the toner carrying state. If the toner carrying state deteriorates, the output value of the toner adhesion amount obtained by the toner adhesion sensor 61 may be erroneous. Specifically, the toner adhesion amount of the part of the toner on the photosensitive drum 51 that adheres to the transfer roller 541 may be detected as low. For this reason, it is preferable that the toner adhesion sensor 61 is installed downstream of the developing device 53 and upstream of the transfer unit 54.

[0024] 3 is a schematic diagram showing the configuration of toner adhesion amount sensor 61. Toner adhesion amount sensor 61 has a light emitting element 62 and a light receiving element 63, and is an optical sensor used for density adjustment. A light source light amount signal is output by control unit 7, and light emitting element 62 irradiates light corresponding to the light source light amount signal onto the toner image carrier (photosensitive drum 51 in FIG. 3). The light receiving element receives reflected light reflected by the toner image carrier and a toner image 64 formed on the toner image carrier, and transmits a reflected light amount signal corresponding to the reflected light to control unit 7.

[0025] Next, a description will be given of the configuration of a control system of the image forming apparatus 10. Fig. 4 is a block diagram showing an outline of an example of the configuration of the control system of the image forming apparatus 10. The operation input unit 1, the reading unit 2, the paper storage unit 3, the conveying unit 4, the image forming unit 5, and the sensor unit 6 have already been described above, so their description will be omitted.

[0026] The control unit 7 comprehensively controls the entire image forming apparatus 10. The control unit 7 realizes various functions by executing programs stored in a program memory such as a ROM (not shown).

[0027] The memory 8 is a storage area to / from which programs and data are input / output by the control unit 7. The memory 8 is configured with a non-volatile memory, and is, for example, an HDD or SSD.

[0028] The I / F unit 9 is an interface for connecting the image forming apparatus 10 to an external device 91, and includes not only wired but also wireless interfaces. The external device 91 is, for example, a smart device, a PC, an external memory, an external server, etc. The external memory is, for example, a USB memory or an SD memory card, and is an external storage memory that is detachable from the image forming apparatus 10. The external server is, for example, a print server that connects the image forming apparatus 10 to a computer network and allows it to be used by multiple PCs.

[0029] The density adjustment control of the image forming apparatus 10 will be described.

[0030] The control unit 7 compares the toner adhesion amount detected by the toner adhesion amount sensor 61 in the density adjustment test pattern 661 with a reference value to determine whether it is within an allowable range that does not interfere with image formation. If it is outside the allowable range, the image formation conditions are changed. For example, when the toner adhesion amount detected by the toner adhesion amount sensor 61 for the toner image formed by the image forming unit 5 under the control of the control unit 7 is significantly different from the actual toner adhesion amount beyond the allowable range, the amount of light of the laser optical unit 52 is changed to correct it. This allows density adjustment.

[0031] The toner image developed for density adjustment control is not transferred to the paper and is scraped off by the cleaning blade 56 .

[0032] The density adjustment control is executed, for example, after a predetermined number of sheets have been printed, or when the image forming apparatus 10 is turned on.

[0033] Fig. 5(a) is a diagram showing a density adjustment test pattern 661 formed on the photosensitive drum 51. The density adjustment test pattern 661 is configured by forming a single toner image. The density adjustment test pattern 661 is formed as a toner image on the photosensitive drum 51. A toner image 644 shown in Fig. 5(a) indicates a toner image with a density of 100% using, for example, black toner.

[0034] FIG. 5(b) is a diagram showing an output waveform of the toner adhesion sensor 61 for the density adjustment test pattern 661. The vertical axis indicates the toner concentration based on the detection result of the toner adhesion sensor 61, and the horizontal axis indicates time. FIG. 5(b) corresponds to the detection result of the density adjustment test pattern 661 shown in FIG. 5(a). An output value 652 is a detection of the leading edge 642 of the toner image 644. An output value 653 is a detection of the trailing edge 643 of the toner image 644. An output value 654 is a detection of the toner adhesion amount of the toner image 644. Time T indicates the time (arrival time) elapsed from the detection start position S to the detection of the reference position of the toner image 644 detected by the toner adhesion sensor 61 due to the rotation of the photosensitive drum 51.

[0035] In density adjustment control, for example, the central portions of leading edge 642 and trailing edge 643 of the toner image shown in Fig. 5(a) are set as reference positions, and the toner adhesion amount at the reference position is compared with the reference value of the toner adhesion amount stored in memory. The reference position may be a position indicating the median value of output value 652 and output value 653 during the time when toner image 644 in Fig. 5(b) is detected. In addition, the reference position is not limited to the central portion of the toner image, and leading edge 642 or the like may be used as the reference position, as long as it is any output value at which the corresponding toner image is detected.

[0036] The test pattern for density adjustment may be a test pattern 662 formed by successively forming toner images of different densities as shown in Fig. 6(a). Since Fig. 6 is Fig. 5 to which toner images of different densities have been added, the same parts as Fig. 5 are given the same numbers and their explanations are omitted. Pattern 645 in Fig. 6(a) shows a toner image of 50% density, and pattern 646 shows a toner image of 25% density. Output values ​​655 and 656 in Fig. 6(b) are the detected toner adhesion amounts of patterns 645 and 655, respectively.

[0037] 6(a) is used to set a reference position, a first output value (first value) and a second output value (second value) corresponding to the leading edge 642 and the trailing edge 643 may be detected in the measurement by the toner adhesion sensor 61. When the output value of the toner concentration detected by the toner adhesion sensor 61 differs from the output value detected immediately before or after by a predetermined value or more, the first output value and the second output value are detected as the edge of the toner image.

[0038] A case where the reference position of the pattern 644 is set in FIG. 6B will be described. For example, a predetermined value for judging the difference between the first output value and the second output value and the output value detected immediately before or after is set to a value of 5% density. Since there is a difference of 100% toner density between the output value 652 and the output value immediately before it, the output value 652 is detected as the first output value, that is, the leading edge. Furthermore, there is a difference of 50% toner density between the output value 653 and the output value immediately after it, so the output value 653 is detected as the second output value, that is, the trailing edge. In this way, the output value 652 and the output value 653 are detected as edges, and the median value of the time corresponding to the output value 652 and the output value 653 detected as edges can be set as the reference position.

[0039] The control unit 7 may detect the leading edge 642 and the trailing edge 643 of the test pattern 662 by the toner adhesion amount sensor 61, and may set any position from when the leading edge 642 is detected to when the trailing edge 643 is detected as the reference position. The control unit 7 calculates an appropriate operation timing for the registration roller 41 based on the arrival time from the detection start position S to the reference position.

[0040] The image forming apparatus 10 according to the embodiment of the present invention detects the amount of toner adhesion in the above-mentioned density adjustment control, and corrects the operation timing of the registration roller 41 by the control unit 7 based on the arrival time from the detection start position S to the detection of the reference position of the toner image. This makes it possible to correct the image writing position. Also, the timing of starting exposure of the photosensitive drum 51 may be corrected based on the arrival time from the detection start position S to the reference position. The detection start position S is based on, for example, the timing when the laser optical unit 52 starts exposing the photosensitive drum 51. The detection start position S may be located downstream of the reference position in the rotation direction of the photosensitive drum 51.

[0041] Control relating to correction of the image writing position (writing position correction control) in the first embodiment will be described with reference to FIG.

[0042] FIG. 7 is a flowchart of the writing position correction control according to the image forming apparatus 10 of the first embodiment.

[0043] First, the image forming unit 5 forms the density adjustment test pattern 661 shown in FIG. 5(a) on the photosensitive drum 51 (ACT100).

[0044] When the density adjustment test pattern 661 is formed on the photosensitive drum 51, the toner adhesion amount sensor 61 measures the amount of toner adhesion on the photosensitive drum 51 from a predetermined detection start position S (ACT101).

[0045] Based on the detection result of the toner adhesion amount sensor 61, the control unit 7 detects the center portions of the leading edge 642 and the trailing edge 643 of the toner image 644 of the test pattern 661 as reference positions (ACT102).

[0046] The control unit 7 calculates the arrival time from a predetermined detection start position S to the reference position of the toner image 644, that is, the time T from the start of detection to the median time between the output value 652 and the output value 653, as shown in Fig. 5(b). The control unit 7 calculates an appropriate operation timing of the registration rollers 41 based on the calculated time T (ACT103).

[0047] The control unit 7 registers the information on the appropriate operation timing of the registration rollers 41 calculated in ACT103 in the memory 8 (ACT104).

[0048] The control unit 7 controls the operation timing of the registration rollers 41 during image formation based on information on appropriate operation timing of the registration rollers 41 registered in the memory 8.

[0049] By such control, the operation timing of the registration rollers 41 can be corrected in the series of operations of the density adjustment control, and the image writing start position can be corrected.

[0050] In the density adjustment control, the image forming apparatus 10 according to the first embodiment can correct the image writing position on the paper to an appropriate position in addition to correcting the density. The correction of the image writing position is realized by controlling the operation timing of the registration roller 41. The means for correcting the image writing position does not require a separate test pattern other than the test pattern for image quality control. In addition, the irradiation start timing of the laser optical unit 52 may be corrected based on the arrival time from the detection start position S to the reference position. At least one of the correction of the irradiation start timing of the laser optical unit 52 and the correction of the operation timing of the registration roller 41 can be corrected in the series of operations of the density adjustment control.

[0051] As the second embodiment, an image forming apparatus 10 using an intermediate transfer method will be described.

[0052] The configuration of the image forming apparatus 10 according to the second embodiment is the same as that of the first embodiment except for the image forming unit 5, and therefore a description thereof will be omitted.

[0053] Fig. 8 is a schematic diagram of an image forming unit 5 according to a second embodiment. In the image forming unit 5 shown in Fig. 8, the same components as those shown in Fig. 2 are designated by the same reference numerals, and descriptions already given thereto will be omitted.

[0054] The image forming unit 5 according to the second embodiment shown in Fig. 8 is of an intermediate transfer type. The difference between the direct transfer type described in the first embodiment and the intermediate transfer type of this embodiment is that in the direct transfer type, the toner image formed on the photosensitive drum 51 is transferred to paper, whereas in the intermediate transfer type, the toner image formed on the photosensitive drum 51 is transferred to a transfer belt 57, and then the toner image on the transfer belt 57 is transferred to paper.

[0055] In the intermediate transfer method, a transfer roller 541 is provided so as to be in contact with a transfer belt 57, and the position where the transfer roller 541 and the transfer belt 57 are in contact with each other is the transfer position 54.

[0056] The transfer belt 57 is a toner image carrier. The transfer belt 57 is an endless belt. The transfer belt 57 is rotated in the direction of the arrow b by a roller. The toner image formed on the photosensitive drum 51 is transferred onto the surface of the transfer belt 57.

[0057] The cleaning blade 56 is disposed downstream of the transfer unit 54 in the rotation direction of the transfer belt 57, and scrapes off and removes waste toner remaining on the transfer belt 57 after transfer. The cleaning blade 56 is also disposed downstream of the contact surface between the transfer belt 57 and the photosensitive drum 51 (not shown), and removes waste toner remaining on the photosensitive drum 51 after transfer.

[0058] In the intermediate transfer type image forming unit 5, the toner adhesion sensor 61 is disposed downstream of the photosensitive drum 51 in the rotation direction of the transfer belt 57. The toner adhesion sensor 61 detects the amount of toner adhesion of the toner image transferred onto the transfer belt 57.

[0059] The writing position correction control according to the second embodiment will be described.

[0060] In the second embodiment, the toner adhesion sensor 61 starts detecting the amount of toner adhesion at the timing when the laser optical unit 52 starts exposing the photosensitive drum 53 (detection start position S). A toner image is formed on the surface of the photosensitive drum 51 by the developing device 53, and the toner image is transferred to the transfer belt 57. The control unit 7 calculates the time T from the detection start position S detected by the toner adhesion sensor 61 to the reference position of the toner image transferred to the transfer belt 57. The control unit 7 calculates an appropriate operation timing for the registration roller 41 based on the time T. The control unit 7 stores the calculated appropriate operation timing for the registration roller 41 in the memory 8. The control unit 7 controls the operation timing of the registration roller 41 based on the appropriate operation timing for the registration roller 41 stored in the memory 8.

[0061] In this manner, the write start position correction control can also be performed in the intermediate transfer type image forming apparatus 10 according to the second embodiment.

[0062] A modification of the second embodiment (second modification) will be described.

[0063] 9 is a schematic diagram showing an image forming unit 5 according to a second modified example. The second modified example is a so-called color multifunction machine, and has multiple types of toner. The configuration of the image forming unit 5 according to the second modified example is the same as that of the second embodiment, except that it has multiple photosensitive drums 51 and developing devices 53, so a description thereof will be omitted. Here, a pair of one photosensitive drum 51 and its corresponding developer 53 is referred to as a station.

[0064] The multiple developing devices 53 shown in Fig. 9 form toner images on the multiple photosensitive drums 51 with toners having different properties. The toners having different properties are, for example, toners of different colors. For example, the toners of different colors are, from the downstream side in the rotation direction of the conveying roller 57 in Fig. 9, black (K), cyan (C), magenta (M), and yellow (Y). The toners having different properties may be toners that can be erased by, for example, heating, exposure to light, or the passage of time.

[0065] In the second modified example, the write start position correction control described in the second embodiment can be performed in each station. This makes it possible to correct the write start position of an image to an appropriate position when forming an image using only one station, that is, when forming an image in a single color.

[0066] In the second modified example, by using the test pattern 663 for density adjustment, the positions of the toner images formed at each station can be corrected so as to coincide with each other (registration correction for each color).

[0067] Fig. 10(a) is a diagram showing a density adjustment test pattern 663 formed on transfer belt 57. The density adjustment test pattern 663 is configured by forming a plurality of toner images having different properties at intervals. Specifically, black (K), cyan (C), magenta (M), and yellow (Y) toner images are formed at intervals. Toner image B, toner image C, toner image M, and toner image Y in Fig. 10(a) are each formed at 100% density, for example.

[0068] FIG. 10B is a diagram showing an output waveform of the toner adhesion sensor 61 for the density adjustment test pattern 663. The vertical axis indicates the toner concentration based on the detection result of the toner adhesion sensor 61, and the horizontal axis indicates time. FIG. 10B corresponds to the detection result of the density adjustment test pattern 663 shown in FIG. 10A. The output value B, the output value C, the output value M, and the output value Y in FIG. 10B are the detected toner adhesion amounts of the toner images B, C, M, and Y in FIG. 10A, respectively. The times TK, TC, TM, and TY indicate the arrival times from the detection start position S to the reference position of the toner image formed by each station, detected by the toner adhesion sensor 61 due to the rotation of the rotating belt 57.

[0069] The registration correction control for each color in the second modified example will be described with reference to FIG.

[0070] FIG. 11 is a flowchart of the color registration correction control performed by the control unit 7.

[0071] First, the image forming unit 5 forms the density adjustment test pattern 663 shown in FIG. 10(a) on the transfer belt 57 (ACT200).

[0072] When the density adjustment test pattern 663 is formed on the transfer belt 57, the toner adhesion amount sensor 61 measures the amount of toner adhesion on the transfer belt 57 from a predetermined detection start position S (ACT 201).

[0073] The control unit 7 detects the reference position of each toner image of the test pattern 663 based on the detection result of the toner adhesion amount sensor 61 (ACT 202).

[0074] The control unit 7 calculates the time TK, the time TC, the time TM, and the time TY, which are the arrival times of each toner image from a predetermined detection start position S to a reference position. The control unit 7 calculates an appropriate exposure timing of the laser optical unit 52 based on each calculated arrival time (ACT203).

[0075] The appropriate exposure timing is, for example, Time TK - Time TC = Time TC - Time TM = Time TM - Time TY It is.

[0076] The control unit 7 registers the information on the appropriate exposure timing of the laser optical unit 52 calculated in ACT 203 in the memory 8 (ACT 204).

[0077] Based on information on the appropriate exposure timing of the laser optical unit 52 registered in the memory 8, the control unit 7 controls the exposure timing of each station of cyan (C), magenta (M), and yellow (Y) by the laser optical unit 52 during image formation.

[0078] With this control, the exposure timing of the laser optical unit 52 can be corrected during a series of operations in density adjustment control, and correction can be performed so that the sub-scanning direction positions of the toner images formed at each station match. Correction of the sub-scanning direction position of each color is achieved by controlling the exposure timing of the laser optical unit 52. In the registration correction control for each color, no other patterns are required other than the test pattern for image quality control.

[0079] In the image forming apparatus 10 according to the second modification, in addition to correcting the density, the density adjustment control can also perform control to correct the position of each color in the sub-scanning direction to an appropriate position.

[0080] In each embodiment and modification, each correction is performed based on the arrival time from the detection start position S to the reference position of the toner image, but the value from the detection start position S to the reference position of the toner image that is used as the basis for correction does not have to be limited to the arrival time. For example, any value that can indicate the relative relationship between the detection start position S and the reference position of the toner image, such as the distance from the detection start position S to the reference position of the toner image, the number of rotations of a stepping motor, or the number of clocks of a clock module, may be used.

[0081] Although various embodiments and modifications of the present invention have been described, these embodiments and modifications are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0082] 5. Image forming section 52 Laser optical unit 661, 662, 663: Test patterns for density adjustment 7. Control section 41 Registration roller 51 Photosensitive drum 54 Transfer section 57 Transfer belt 61 Toner adhesion amount sensor

Claims

1. a laser optical unit that forms a latent image by irradiating light; an image carrier that carries a developer image and moves the carried developer image in a predetermined direction; an image forming section that forms the latent image formed on the image carrier by the laser optical unit as a developer image on the image carrier by using a developer; a developer adhesion amount sensor that detects a value indicating a developer concentration based on an amount of developer adhesion in a pattern image for detecting a developer concentration in which a plurality of developer images having different densities are formed on the image carrier by the image forming unit and are continuous in the predetermined direction; a transfer section for transferring the developer image formed on the image carrier onto a sheet of paper; A registration roller for conveying the paper to the transfer unit at a predetermined timing; a control unit having a first control that detects a leading edge and a trailing edge in the predetermined direction of the developer image of the predetermined density based on a detection result of the developer adhesion amount sensor and a predetermined value set according to a density difference between the developer image of the predetermined density and a developer image successive to the developer image of the predetermined density in the pattern image in order to detect an edge of the developer image of the predetermined density in the pattern image, and that is capable of correcting a timing at which the registration roller operates to transport a sheet onto which the developer image formed by the image forming unit is transferred from a stagnant state based on a relative value from a predetermined detection start position to the reference position, with a central portion from the leading edge to the trailing edge being set as a reference position; An image forming apparatus comprising:

2. the developer adhesion amount sensor detects a plurality of values ​​as toner concentrations from a plurality of continuous developer images having different densities in the pattern image formed on the image carrier moving in the predetermined direction, the control unit determines a position where a difference between a value detected by the developer adhesion amount sensor and a value detected immediately before the detection of the developer adhesion amount sensor is equal to or greater than the predetermined value as the leading edge, and determines a position where a difference between a value detected by the developer adhesion amount sensor after detecting the leading edge and a value detected immediately after the detection of the developer adhesion amount sensor is equal to or greater than the predetermined value as the trailing edge. The image forming apparatus according to claim 1 .

3. the control unit is capable of the first control when performing density adjustment control for correcting a developer image formed on an image carrier using the pattern image so that the developer image has an appropriate density.

3. The image forming apparatus according to claim 1 or 2.

Images