Image forming apparatus

Abstract

To provide an image forming apparatus capable of appropriately correcting the deviation of writing start timing at the time of gain switching, correcting the deviation by a correction value corresponding to the image forming apparatus and reducing costs.SOLUTION: An image forming apparatus comprising: a light emitting element configured to emit light; a deflector configured to deflect the light to scan a photosensitive member; a light detecting element configured to detect the light to determine a write start timing for forming a latent image; a sensitivity switching circuit configured to switch to a sensitivity of the light detecting element; and a control unit, the control unit includes a light emission control unit that controls a light amount of light emitted by the light emitting element, a sensitivity switching unit that switches a sensitivity according to a set light amount, a correction unit that corrects a deviation of a writing start timing using characteristic value information indicating a relationship between the light amount and a change amount of the writing start timing, and an update unit that calculates the change amount of the writing start timing while switching to each sensitivity and updates a characteristic value constituting the characteristic value information based on the change amount.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Known electrophotographic image forming apparatuses use laser diodes to expose a photoconductor. In these image forming apparatuses, laser light emitted from the laser diode is reflected by a rotating polygon mirror. As the laser light is irradiated from one end of the polygon mirror to the other, it is deflected according to the angle of the polygon mirror and scans one line across the photoconductor. An electrostatic latent image of one line is formed on the photoconductor by switching the laser diode on and off according to input image data. The image forming apparatus then forms a desired electrostatic latent image by repeatedly performing line scans while rotating the photoconductor. In this case, the image forming apparatus must synchronize the write start timing for starting image formation when repeating line scans. To determine this write start timing, the image forming apparatus is configured to have a photodetector installed immediately before scanning the photoconductor to detect the scanning position of the laser light. The image forming apparatus determines the write start timing for image data based on the output signal of the photodetector. The photodetector includes a photodiode and detects minute current changes using gain. The light detection sensor determines whether or not laser light is being input based on changes in the current. The amount of laser light changes depending on conditions. For example, such conditions include changes in the resolution of the output image, changes in productivity (linear speed), and changes in the temperature environment. As a result, changes in the amount of laser light from the laser diode also change the amount of laser light input to the light detection sensor. When the amount of laser light changes, the magnitude of the current flowing through the light detection sensor changes, causing a change in the detection waveform. When the detection waveform of the light detection sensor changes, the timing at which image data starts to be written shifts, causing a positional shift in the scanning direction (main scanning direction). This positional shift, especially in color machines, causes changes in color tone and color shift, degrading image quality.

[0003] In addition, a shift in the write start timing can also occur when the gain of the optical detection sensor is switched. As described above, the amount of laser light changes depending on the conditions, and the amount of laser light entering the optical detection sensor also changes within that range. In this case, the gain must be set so that the laser light can be detected regardless of the light amount. However, if the range of light amount changes is wide, a single gain setting may not be enough to cover it. If the gain is set too small, the laser light will not be detected properly. Conversely, if the gain is set too large, stray light or flare light will enter the optical detection sensor, resulting in false detection. To avoid these abnormal operations, the gain is switched to a high gain when the amount of laser light is low and to a low gain when the amount of laser light is high. Switching the gain in this way enables stable detection of the laser light. However, switching the gain significantly changes the waveform of the optical detection sensor's detection signal, shifting the timing at which image data write starts and causing misalignment in the scanning direction (main scanning direction).

[0004] As a technique for dealing with such a discrepancy in the timing at which writing starts, for example, a configuration has been disclosed in which a gain change circuit has a second gain that can be used in a second light intensity range that includes a light intensity range lower than the first light intensity range, and changes the gain to the first gain or the second gain so that a signal is output within a target time after light is incident on the light detection unit (for example, Patent Document 1).

[0005] In addition, a configuration has been disclosed in which, in line scanning, the amount of correction for the timing at which image data is written is calculated based on two measurement results: the interval between synchronous detection signals when the gain is constant, and the interval between synchronous detection signals when the gain is switched midway (for example, Patent Document 2).

[0006] Also disclosed is a configuration for adding a correction value (second control value) for the deviation in the write start timing, which changes depending on the light intensity setting value of the light beam, to the resist correction value (first control value), a configuration for switching the gain to correct the deviation, and a detailed method for calculating the second control value (for example, Patent Document 3). Summary of the Invention [Problem to be solved by the invention]

[0007] However, the technology described in Patent Document 1 has a problem in that it cannot prevent image quality degradation due to a shift in the write start timing that occurs when gain is switched. Furthermore, the technology described in Patent Document 2 requires a function to measure the interval between synchronization detection signals in line scanning, which requires a logic circuit for measurement, complicating implementation and unavoidably increasing costs. Furthermore, the technology described in Patent Document 3 determines correction values ​​in advance, and these values ​​change due to variations in the characteristics of components installed in the optical writing device, which means that it is not possible to apply optimal correction values ​​tailored to each individual image forming device.

[0008] The present invention has been made in consideration of the above, and aims to provide an image forming device that can appropriately correct the deviation in the timing of starting writing when switching gain, correct the deviation using a correction value corresponding to the image forming device, and reduce costs. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems and achieve the object, the present invention provides an image forming apparatus comprising: a light-emitting element that irradiates light; a deflector that deflects the light irradiated from the light-emitting element and scans it onto a photosensitive element; a light-detecting element that detects the light in order to determine a write start timing for forming a latent image by scanning the light irradiated from the light-emitting element via the deflector onto the photosensitive element; a sensitivity switching circuit that switches the sensitivity of the light-detecting element to one of a plurality of sensitivities for detecting the light; and a control unit that controls the operation of the image forming apparatus, wherein the control unit comprises: a light-emitting control unit that controls the amount of light irradiated by the light-emitting element; a sensitivity switching unit that switches the sensitivity via the sensitivity switching circuit in accordance with the set light amount; a correction unit that corrects a deviation in the write start timing using characteristic value information that indicates the relationship between the light amount and an amount of change in the write start timing; and an update unit that calculates an amount of change in the write start timing while being switched to each of the sensitivities by the sensitivity switching unit, and updates characteristic values ​​that constitute the characteristic value information based on the amount of change. [Effects of the Invention]

[0010] According to the present invention, it is possible to appropriately correct the deviation in the timing at which writing starts when gains are switched, correct the deviation using a correction value that corresponds to the image forming apparatus, and reduce costs. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating the operation of forming a color matching pattern and correcting color misregistration in the image forming apparatus according to the embodiment. [Figure 3] FIG. 3 is a diagram illustrating a scanning operation of a laser beam in the image forming apparatus according to the embodiment. [Figure 4] FIG. 4 is a diagram illustrating the operation of laser light being incident on the light detection sensor of the image forming apparatus according to the embodiment. [Figure 5] FIG. 5 is a diagram illustrating a detection signal and an output signal in the light detection sensor of the image forming apparatus according to the embodiment. [Figure 6] FIG. 6 is a diagram illustrating an example of the configuration of an optical writing device of an image forming apparatus according to an embodiment. [Figure 7] FIG. 7 is a diagram showing another example of the configuration of the optical writing device of the image forming apparatus according to the embodiment. [Figure 8] FIG. 8 is a diagram illustrating the relationship between the amount of laser light incident on the light detection sensor of the image forming apparatus according to the embodiment, and the detection signal and output signal. [Figure 9] FIG. 9 is a diagram showing an example of the configuration of the synchronization detection plate of the image forming apparatus according to the embodiment. [Figure 10] FIG. 10 is a diagram illustrating a shift in the write start timing when the gain is switched in the image forming apparatus according to the embodiment. [Figure 11] FIG. 11 is a diagram illustrating an example of the functional block configuration of the control device of the image forming apparatus according to the embodiment. [Figure 12] FIG. 12 is a diagram illustrating a case where the gain is switched to prevent erroneous detection of stray light for the synchronization detection plate of the image forming apparatus according to the embodiment. [Figure 13] FIG. 13 is a diagram illustrating a case where the gain is switched to prevent missed detection for the synchronization detection plate of the image forming apparatus according to the embodiment. [Figure 14] FIG. 14 is a diagram illustrating an example of the characteristic value table. [Figure 15] FIG. 15 is a diagram illustrating an example of how to use the characteristic value table. [Figure 16] FIG. 16 is a diagram illustrating an example of a characteristic value curve of a polynomial. [Figure 17] FIG. 17 is a diagram for explaining how to determine the resistance that determines the value of the gain resistor of the light detection sensor. [Figure 18] FIG. 18 is a diagram for explaining an outline of the operation of the characteristic value update process of the image forming apparatus according to the embodiment. [Figure 19]FIG. 19 is a flowchart showing an example of the flow of the characteristic value update process of the image forming apparatus according to the embodiment. [Figure 20] FIG. 20 is a diagram illustrating the operation of estimating a curve of the amount of change in the write start timing from the measurement results in the image forming apparatus according to the embodiment. [Figure 21] FIG. 21 is a diagram illustrating the operation of estimating a curve (second curve) of the amount of change in the write start timing from the measurement results in the image forming apparatus according to the embodiment. [Figure 22] FIG. 22 is a diagram illustrating updating of the characteristic value table in the image forming apparatus according to the embodiment. [Figure 23] FIG. 23 is a diagram illustrating updating of the characteristic value curve in the image forming apparatus according to the embodiment. [Figure 24] FIG. 24 is a flowchart showing an example of the flow of the color matching operation of the image forming apparatus according to the embodiment. [Figure 25] FIG. 25 is a flowchart showing an example of the flow of the printing operation of the image forming apparatus according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of an image forming apparatus according to the present invention will be described in detail with reference to the drawings. Furthermore, the present invention is not limited to the following embodiments, and the components in the following embodiments include those that would be easily conceived by a person skilled in the art, those that are substantially the same, and those that are within the scope of what is called equivalents. Furthermore, various omissions, substitutions, modifications, and combinations of the components can be made without departing from the spirit of the following embodiments.

[0013] (Configuration of image forming device) FIG. 1 is a diagram showing an example of the configuration of an image forming apparatus according to an embodiment. FIG. 2 is a diagram explaining the operation of forming a color matching pattern and correcting color misregistration in the image forming apparatus according to an embodiment. FIG. 3 is a diagram explaining the laser light scanning operation in the image forming apparatus according to an embodiment. FIG. 4 is a diagram explaining the operation of laser light being incident on the light detection sensor of the image forming apparatus according to an embodiment. FIG. 5 is a diagram explaining the detection signal and output signal in the light detection sensor of the image forming apparatus according to an embodiment. The configuration of the image forming apparatus 1 according to this embodiment will be described with reference to FIGS. 1 to 5.

[0014] 1 is a device that transfers toner onto recording paper to form a print. Image forming device 1 is a tandem type device that forms a full-color image by overlaying four colors (cyan, magenta, yellow, and black), for example.

[0015] 1, image forming apparatus 1 includes control device 10 (controller), optical writing device 20, four photosensitive drums 30a, 30b, 30c, and 30d, four cleaning units 31a, 31b, 31c, and 31d, four charging devices 32a, 32b, 32c, and 32d, four developing rollers 33a, 33b, 33c, and 33d, and four toner cartridges 34a, 34b, 34c, and 34d. Furthermore, as shown in FIG. 1, image forming apparatus 1 includes transfer belt 40, transfer roller 42, density detector 45 (detector), four home position sensors 46a, 46b, 46c, and 46d, fuser roller 50, paper feed roller 54, registration roller pair 56, paper discharge roller 58, paper feed tray 60, paper discharge tray 70, and communication control device 80.

[0016] The photosensitive drum 30a, cleaning unit 31a, charging device 32a, developing roller 33a, and toner cartridge 34a are used as a set, and these constitute an image forming station (sometimes called a K station) that forms a black (K) image.

[0017] The photosensitive drum 30b, cleaning unit 31b, charging device 32b, developing roller 33b, and toner cartridge 34b are used as a set, and they constitute an image forming station (sometimes called a C station) that forms a cyan (C) image.

[0018] The photosensitive drum 30c, cleaning unit 31c, charging device 32c, developing roller 33c, and toner cartridge 34c are used as a set, and these constitute an image forming station (sometimes referred to as an M station) that forms a magenta (M) image.

[0019] The photosensitive drum 30d, cleaning unit 31d, charging device 32d, developing roller 33d, and toner cartridge 34d are used as a set, and they constitute an image forming station (sometimes called a Y station) that forms a yellow (Y) image.

[0020] Note that photosensitive drums 30a, 30b, 30c, and 30d may be referred to simply as "photosensitive drum 30" (photosensitive body) when referring to any one of the photosensitive drums or when collectively referring to the same. Also, cleaning units 31a, 31b, 31c, and 31d may be referred to simply as "cleaning unit 31" when referring to any one of the cleaning units or when collectively referring to the same. Also, charging devices 32a, 32b, 32c, and 32d may be referred to simply as "charging device 32" when referring to any one of the charging devices or when collectively referring to the same. Also, developing rollers 33a, 33b, 33c, and 33d may be referred to simply as "developing roller 33" when referring to any one of the developing rollers or when collectively referring to the same. Also, toner cartridges 34a, 34b, 34c, and 34d may be referred to simply as "toner cartridge 34" when referring to any one of the toner cartridges or when collectively referring to the same. Furthermore, when referring to any one of the home position sensors 46a, 46b, 46c, and 46d or when referring to them collectively, they may be simply referred to as "home position sensor 46."

[0021] The control device 10 is a control device that comprehensively controls each device provided in the image forming apparatus 1. The control device 10 has a CPU (Central Processing Unit), a ROM (Read Only Memory) that stores programs written in code executed by the CPU and various data used when executing the programs, a RAM (Random Access Memory) that is a working memory, and an AD conversion circuit that converts analog data to digital data. The control device 10 also controls each device in response to a request from the upper device 2 and sends image data from the upper device 2 to the optical writing device 20. The upper device 2 is an information processing device such as a PC (Personal Computer) or a workstation that sends a print job including image data to be printed to the control device 10 via a communication control device 80. The configuration and operation of the control device 10 will be described in detail later with reference to FIG. 11.

[0022] The optical writing device 20 is an optical device that irradiates the surfaces of the corresponding charged photosensitive drums 30 (photoconductors) with laser light modulated for each color based on image data (cyan image data, magenta image data, yellow image data, and black image data). As a result, the charge on the surface of each photosensitive drum 30 is lost only in the areas irradiated with the light, and an electrostatic latent image corresponding to the image data is formed on the surface of each photosensitive drum 30. The electrostatic latent image formed on the surface of each photosensitive drum 30 moves toward the corresponding developing roller 33 as the photosensitive drum 30 rotates. The detailed configuration of the optical writing device 20 will be described later with reference to FIGS. 6 and 7.

[0023] The photosensitive drum 30 is an example of a latent image carrier, and is a drum-shaped member with a photosensitive layer formed on its surface. That is, the surface of the photosensitive drum 30 is the surface to be scanned. The photosensitive drums 30a, 30b, 30c, and 30d are arranged side by side, for example, with their rotation axes parallel to each other, and rotate in the same direction (for example, the direction of the arrow shown in FIG. 1).

[0024] In this description, in an XYZ three-dimensional Cartesian coordinate system, the direction parallel to the central axis of each photosensitive drum 30 is the Y-axis direction, and the direction along the arrangement direction of each photosensitive drum 30 is the X-axis direction.

[0025] The cleaning unit 31 is a unit that removes toner (residual toner) remaining on the surface of the corresponding photosensitive drum 30. After the residual toner has been removed, the surface of the photosensitive drum 30 returns to a position facing the corresponding charging device 32 again.

[0026] The charging devices 32 are devices that uniformly charge the surfaces of the corresponding photosensitive drums 30 .

[0027] As the developing roller 33 rotates, toner from the corresponding toner cartridge 34 is applied thinly and uniformly to its surface. When the toner on the surface of the developing roller 33 comes into contact with the surface of the corresponding photosensitive drum 30, it adheres to the portion of the surface that is irradiated with light. In other words, the developing roller 33 causes the toner to adhere to the electrostatic latent image formed on the surface of the corresponding photosensitive drum 30, making it visible and forming a toner image.

[0028] Toner cartridge 34a is a cartridge that supplies black toner to developing roller 33a. Toner cartridge 34b is a cartridge that supplies cyan toner to developing roller 33b. Toner cartridge 34c is a cartridge that supplies magenta toner to developing roller 33c. Toner cartridge 34d is a cartridge that supplies yellow toner to developing roller 33d.

[0029] The transfer belt 40 is a belt that is looped around a belt rotation mechanism and rotates in a fixed direction. The outer surface of the transfer belt 40 contacts the surface of each photosensitive drum 30 at a position opposite the optical writing device 20, and the toner images on each photosensitive drum 30 are sequentially transferred in a superimposed manner to form a color toner image. The outer surface of the transfer belt 40 also contacts a transfer roller 42.

[0030] The transfer roller 42 is a roller that comes into contact with the outer surface of the transfer belt 40 via the recording paper, and transfers the color toner image formed on the transfer belt 40 onto the recording paper.

[0031] The density detector 45 is a sensor (TM sensor) that detects the toner density of the color toner image on the transfer belt 40 and is disposed on the -X side (downstream of the four photosensitive drums 30) facing the transfer belt 40. For example, as shown in FIG. 2, a plurality of density detectors 45 are installed in a direction (main scanning direction) perpendicular to the moving direction of the transfer belt 40. When performing color matching, the image forming apparatus 1 forms a color matching pattern so that it passes through the detection position of each density detector 45 and causes each density detector 45 to detect it. Then, the image forming apparatus 1 uses the detection results of each density detector 45 to calculate correction values ​​for correcting registration misalignment and magnification misalignment between colors. The correction value for the write start timing is included in one of the correction values.

[0032] The home position sensor 46 is a sensor that detects the home position (original position) of the rotation of the corresponding photosensitive drum 30 .

[0033] The fixing roller 50 applies heat and pressure to the recording paper to fix the toner onto the recording paper. The recording paper with the fixed toner is sent to the paper discharge tray 70 via the paper discharge roller 58, and is stacked on the paper discharge tray 70 in order.

[0034] The paper feed roller 54 is disposed near the paper feed tray 60 and is a member that takes out recording paper one by one from the paper feed tray 60 and conveys it to the pair of registration rollers 56 .

[0035] The registration roller pair 56 is a pair of rollers that feeds the recording paper toward the gap between the transfer belt 40 and the transfer roller 42 at a predetermined timing. This causes the color toner image on the transfer belt 40 to be transferred onto the recording paper. The recording paper after the transfer is then sent to the fixing roller 50.

[0036] The paper discharge roller 58 is a roller that discharges the recording paper onto which the color toner image has been transferred, sent from the fixing roller 50, onto a paper discharge tray 70.

[0037] The paper feed tray 60 is a tray for storing recording paper. The paper discharge tray 70 is a tray for stacking recording paper onto which a color toner image has been transferred and which has been discharged from the paper discharge roller 58.

[0038] The communication control device 80 is a device that controls two-way communication with a higher-level device 2 (e.g., a computer) via a network, etc. The communication control device 80 realizes communication that complies with, for example, the TCP (Transmission Control Protocol) / IP (Internet Protocol) standard or the USB (Universal Serial Bus) standard.

[0039] 3, the image forming apparatus 1 is also provided with a synchronization detection plate 90 having a light detection sensor 91 (light detection element) mounted thereon to detect the laser light scanned from the optical writing device 20 onto each photosensitive drum 30. That is, the image forming apparatus 1 is provided with a synchronization detection plate 90 for each photosensitive drum 30. For the sake of simplicity, FIG. 3 illustrates the synchronization detection plate 90 as being disposed on an extension of the axis of the photosensitive drum 30. The actual arrangement of the synchronization detection plate 90 will be described later with reference to FIGS. 6 and 7. The light detection sensor 91 mounted on the synchronization detection plate 90 is disposed on the scanning path of the laser light from the optical writing device 20.

[0040] The optical detection sensor 91 is a sensor that detects the laser light immediately before or after a single scan of the laser light by the optical writing device 20 across the photosensitive drum 30 and outputs a synchronization signal. The optical detection sensor 91 is composed of a semiconductor element, such as a photodiode, that generates a current when exposed to light. As shown in FIG. 4, the optical detection sensor 91 includes a lens 91a, a light receiving unit 91b, and a comparator (not shown). Note that the optical detection sensor 91 may be provided with a slit to reduce ambient light and limit the direction of incident light in order to improve detection accuracy.

[0041] The lens 91a is an optical element for narrowing the direction of incident light. When laser light is incident on the light receiving unit 91b, the light receiving unit 91b generates a current, which is amplified by a built-in operational amplifier circuit. The amplified current then flows through a variable gain resistor (described later) and becomes a detection signal from the light detection sensor 91. The comparator compares the detection signal, which is an analog value, with a predetermined constant voltage (threshold shown in FIG. 5) and converts the period during which the constant voltage is exceeded into an output signal (synchronization signal) with a digital value that indicates the detection period during which laser light is detected. In the example shown in FIG. 5, the output signal (synchronization signal) is low level during the period when the constant voltage (threshold) is exceeded and high level during the period when the voltage is not exceeded.

[0042] Then, the optical detection sensor 91 outputs an output signal (synchronization signal) of a digital value to the control device 10. Then, based on the synchronization signal output from the optical detection sensor 91, the control device 10 determines the timing at which the optical writing device 20 starts writing laser light onto the photosensitive drum 30.

[0043] (Configuration of optical writing device) Fig. 6 is a diagram showing an example of the configuration of an optical writing device of an image forming apparatus according to an embodiment. Fig. 7 is a diagram showing another example of the configuration of an optical writing device of an image forming apparatus according to an embodiment. The configuration of the optical writing device 20 of the image forming apparatus 1 according to this embodiment will be described with reference to Figs. 6 and 7.

[0044] 6, the optical writing device 20 includes laser diodes 21a and 21b (examples of light-emitting elements), lenses 22a and 22b, a polygon mirror 23 (deflector), fθ lenses 24a and 24b, mirrors 25a and 25b, and lenses 26a and 26b. The optical writing device 20 further includes a polygon motor 23a shown in FIG. 11, which will be described later.

[0045] The laser diodes 21a and 21b are units that emit laser light. The laser diodes 21a and 21b are controlled by a light emission control unit 102, which will be described later, to turn on and off the laser light, thereby controlling the amount of light emitted from the laser diodes 21a and 21b. The laser light emitted from the laser diodes 21a and 21b reaches each photosensitive drum 30 via each optical system, which will be described later.

[0046] The lenses 22a and 22b are lenses that collimate the laser beams emitted from the laser diodes 21a and 21b, respectively, by using refraction.

[0047] The polygon mirror 23 is rotated by the drive of a polygon motor 23a (described later) and is a rotary polygonal mirror having a polygonal prism shape when viewed in the direction of the rotation axis. The polygon mirror 23 rotates at a predetermined rotation speed and reflects (deflects) the laser light incident thereon after passing through each of the lenses 22a and 22b toward each of the fθ lenses 24a and 24b, thereby repeatedly scanning the laser light in the main scanning direction (the axial direction of the photosensitive drum 30). The laser light scanned in the main scanning direction by the rotation of the polygon mirror 23 is reflected by mirrors 25a and 25b, respectively, and is incident on synchronization detection plates 90a and 90b before or after scanning the photosensitive drum 30.

[0048] The fθ lenses 24a and 24b are lenses that cause the laser light, which is reflected by the polygon mirror 23 and scanned at a constant angular velocity, to scan at a constant speed on each photosensitive drum 30. The polygon mirror 23 and the fθ lenses 24a and 24b repeatedly scan the laser light in the main scanning direction on each photosensitive drum 30, thereby forming an electrostatic latent image (latent image) according to image data on each photosensitive drum 30. The electrostatic latent image is formed so as to spread from the center of the photosensitive drum 30, and the outer area where an image cannot be formed is treated as a non-image area.

[0049] The mirrors 25a and 25b are members that reflect the laser light scanned in the main scanning direction by the rotation of the polygon mirror 23 to the lenses 26a and 26b, respectively, before or after the laser light is scanned onto the photosensitive drum 30.

[0050] The lenses 26a and 26b are lenses that allow the laser beams reflected from the mirrors 25a and 25b to be incident on the synchronization detection plates 90a and 90b, respectively.

[0051] The synchronization detection plates 90a and 90b are the synchronization detection plates 90 described above, and are arranged outside the image area in the main scanning direction of the laser light on the surface of each photosensitive drum 30 and on the start or end point side in the main scanning direction of the laser light scan. The synchronization detection plates 90a and 90b each have a light detection sensor 91, and the light detection sensor 91 detects the respective laser light and outputs the detected light to the control device 10 as a synchronization signal.

[0052] As described above, the laser beams emitted from the laser diodes 21a and 21b pass through the lenses 22a and 22b, the polygon mirror 23, and the fθ lenses 24a and 24b in this order, and reach the photosensitive drum 30, forming electrostatic latent images of the respective colors on the photosensitive drum 30. As shown in FIG. 3 above, the optical writing device 20 controls the amount of laser beam emitted from the laser diode 21 to be constant while scanning the laser beam in one direction.

[0053] 6 shows two laser diodes 21a and 21b, but the optical writing device 20 has a separate laser diode 21 for each color, and causes each laser diode 21 to emit laser light onto different surfaces of the polygon mirror 23 or at different angles of incidence on the same surface, and the laser light passes through a corresponding fθ lens (fθ lenses 24a and 24b in FIG. 6) to scan the photosensitive drum 30 corresponding to each laser diode 21. The optical writing device 20 also has a separate synchronization detection plate 90 corresponding to each laser diode 21. The light detection sensor 91 of each synchronization detection plate 90 detects the laser light from the laser diode 21 for each color and outputs a synchronization signal for each color to the control device 10.

[0054] The configuration of the optical writing device 20 shown in FIG. 6 is an example, and other optical systems may be provided.

[0055] Alternatively, a common synchronization signal may be used for each scanning direction. For example, in FIG. 6, there are two scanning directions: one where the laser beam is irradiated onto the upper side of the polygon mirror 23, and the other where the laser beam is irradiated onto the lower side. Each of the four colors may be classified according to which of the two scanning directions it falls into, and for the two colors that share a common scanning direction, the writing start timing may be determined based on a synchronization signal detected by the laser beam of one of the colors. This allows the number of synchronization detection plates 90 to be reduced from four to two.

[0056] 6, the optical writing device 20 may be configured as a single synchronization detection plate 90, as shown in FIG. 7. In the optical writing device 20 shown in FIG. 7, the laser beams of two laser diodes 21a and 21b, which are scanned to form electrostatic latent images of different colors on the photosensitive drums 30, are incident on a single synchronization detection plate 90 (i.e., a light detection sensor 91) at different angles. By adopting a configuration in which the laser beams are consolidated into a single synchronization detection plate 90, costs can be reduced.

[0057] (Configuration and operation of synchronous detection plate) Fig. 8 is a diagram illustrating the relationship between the amount of laser light incident on the light detection sensor of the image forming apparatus according to the embodiment, and the detection signal and output signal. Fig. 9 is a diagram illustrating an example of the configuration of a synchronization detection plate of the image forming apparatus according to the embodiment. Fig. 10 is a diagram illustrating a shift in the write start timing when the gain is switched in the image forming apparatus according to the embodiment. The configuration and operation of the synchronization detection plate 90 of the image forming apparatus 1 according to the present embodiment will be described with reference to Figs. 8 to 10.

[0058] When the amount of laser light incident on the optical detection sensor 91 of the synchronization detection plate 90 fluctuates, the detection signal also changes. As shown in FIG. 8, if the amount of laser light is strong, the detection signal, which is an analog value, increases, and if the amount of light is weak, the detection signal decreases. As a result, the laser light detection period during which the output signal of the optical detection sensor 91 is at a low level increases or decreases. The image forming apparatus 1 uses the falling edge or rising edge of the output signal (synchronization signal) as the detection position of the laser light incident on the optical detection sensor 91. Therefore, if the amount of laser light increases or decreases, the edge position fluctuates, causing a shift in the write start timing.

[0059] 4, if the angle of the laser light incident on the light detection sensor 91 is tilted, the detection signal from the light detection sensor 91 becomes distorted and not symmetrical. In this case, increasing or decreasing the amount of laser light causes the amount of change in the rising and falling edges of the output signal to become uneven. This makes it impossible to determine the timing that should be used as the reference for detecting the laser light, making it difficult to suppress deviations in the write start timing caused by changes in the amount of laser light incident on the light detection sensor 91.

[0060] Furthermore, there are variations in the assembly of the parts of the optical writing device 20. For example, even a slight change in the mounting angle of the synchronization detection plate 90 may change the angle at which the laser light is incident on the light detection sensor 91. This changes the amount of change in the rising edge and falling edge (right side) of the output signal when the amount of laser light is increased or decreased, and the deviation in the writing start timing varies for each individual optical writing device 20.

[0061] In this embodiment, a configuration is provided that can appropriately correct the deviation in the write start timing regardless of the cause of the deviation in the write start timing as described above.

[0062] As shown in FIG. 9, the synchronization detection board 90 includes a photodetection sensor 91 and a gain switching circuit 92 (sensitivity switching circuit). The gain switching circuit 92 is a circuit for switching the gain for adjusting the detection sensitivity of the photodetection sensor 91 according to two types of gain switching signals SIG1 and SIG2 input from the control device 10. The gain switching circuit 92 includes a resistor R1, a resistor R2, a resistor R3, a switching element SW1, and a switching element SW2.

[0063] In such a synchronization detection board 90, the value of the gain resistor of the photodetection sensor 91 is switched by two types of gain switching signals SIG1 and SIG2 (signals input to the bases of the switching elements SW1 and SW2 respectively) input from the control device 10. In the synchronization detection board 90 shown in FIG. 9, for example, when both of the two types of gain switching signals SIG1 and SIG2 input from the control device 10 are at a low-level voltage, the value of the gain resistor becomes the value of the resistor R1. Also, when the gain switching signal SIG1 input to the base of the switching element SW1 from the control device 10 is at a high-level voltage and the gain switching signal SIG2 input to the base of the switching element SW2 is at a low-level voltage, the gain resistor becomes the resistor when R1 and R2 are connected in parallel, and its value is 1 / (1 / R1 + 1 / R2) < R1). Further, when both of the two types of gain switching signals SIG1 and SIG2 input from the control device 10 are at a high-level voltage, the gain resistor becomes the resistor when R1, R2, and R3 are connected in parallel, and its value is 1 / (1 / R1 + 1 / R2 + 1 / R3) < 1 / (1 / R1 + 1 / R2).

[0064] Note that the gain switching circuit 92 shown in FIG. 9 is configured as an external circuit for the photodetection sensor 91, but it is not limited thereto and may be a circuit built into the photodetection sensor 91. Hereinafter, the gain switching circuit 92 will be described as an external circuit for the photodetection sensor 91.

[0065] Furthermore, as long as there is a function to switch the gain (sensitivity) of the light detection sensor 91, the gain switching signal is not limited to a high-level or low-level voltage as shown in FIG. 9, and the gain may be switched by, for example, a command-type control signal.

[0066] Furthermore, although the gain switching circuit 92 shown in FIG. 9 is configured as a parallel circuit of resistors, the present invention is not limited to this, and the gain may be switched by combining it with a series circuit of resistors.

[0067] As shown in FIG. 10(a), when the amount of laser light incident on the light detection sensor 91 changes, the rising and falling edges of the output signal from the light detection sensor 91 shift, causing a change in the write start timing. This change in write start timing, as shown in FIG. 10(b), results in a nonlinear graph. When the amount of light is small, the peak value of the detection signal from the light detection sensor 91 approaches the reference voltage, resulting in high sensitivity to changes in light amount and a sufficiently large change in the write start timing. On the other hand, when the amount of light is large, the peak value of the detection signal from the light detection sensor 91 exceeds the reference voltage, resulting in low sensitivity to changes in light amount and a small change in the write start timing. Furthermore, as shown in FIG. 10(b), the change in the write start timing curve (graph) varies depending on the sensitivity (gain) of the light detection sensor. When the sensitivity (gain) is large, the detection signal from the light detection sensor 91 increases, making it easier for the peak value to reach the reference voltage. Therefore, as shown in FIG. 10(b), the graph of the change in write start timing (the graph for large gain in FIG. 10(b)) shifts to the left. On the other hand, if the sensitivity (gain) is small, the detection signal of the light detection sensor 91 becomes small and the peak value is less likely to reach the reference voltage, so the graph of the change in the write start timing (the graph for small gain shown in FIG. 10(b)) shifts to the right. In this way, the graph of the change in the write start timing changes as the sensitivity (gain) of the light detection sensor 91 is switched.

[0068] Furthermore, the magnitude of the voltage of the detection signal from the light detection sensor 91 of the synchronization detection plate 90 is generally proportional to the product of the amount of incident laser light P and the gain resistor value G. Therefore, the voltage of the detection signal when the gain resistor value G is constant and the amount of incident laser light P is increased by a factor of α is the same as the voltage of the detection signal when the gain resistor value G is constant and the gain resistor value G is increased by a factor of α. The image forming apparatus 1 according to this embodiment utilizes this property to estimate the amount of change in the writing start timing without changing the amount of laser light by changing (switching) the gain (sensitivity) of the light detection sensor 91 instead of changing the amount of laser light when the amount of laser light incident on the light detection sensor 91 varies within a specific range during use of the image forming apparatus 1. This allows a change amount calculation pattern (described later) to be formed without changing the amount of laser light, thereby enabling the amount of change in the writing start timing to be estimated with high accuracy over the entire range of laser light amounts used in the image forming apparatus 1.

[0069] (Configuration and operation of the control device's functional blocks) FIG. 11 is a diagram showing an example of the configuration of functional blocks of a control device of an image forming apparatus according to an embodiment. FIG. 12 is a diagram illustrating a case where a gain is switched to prevent erroneous detection of stray light for a synchronous detection plate of an image forming apparatus according to an embodiment. FIG. 13 is a diagram illustrating a case where a gain is switched to prevent missed detection for a synchronous detection plate of an image forming apparatus according to an embodiment. FIG. 14 is a diagram showing an example of a characteristic value table. FIG. 15 is a diagram illustrating an example of a method for using the characteristic value table. FIG. 16 is a diagram showing an example of a polynomial characteristic value curve. FIG. 17 is a diagram illustrating a method for determining a resistor that determines the value of the gain resistor of a light detection sensor. The configuration and operation of functional blocks of a control device 10 of an image forming apparatus 1 according to this embodiment will be described with reference to FIGS. 11 to 17.

[0070] As shown in FIG. 11, the control device 10 includes a sensor control unit 101, a light emission control unit 102, a counting unit 103, a deflection control unit 104, a correction value calculation unit 105 (correction unit), a gain switching unit 106 (sensitivity switching unit), a characteristic value processing unit 107 (updating unit), a reference value memory unit 111, a correction value memory unit 112, a gain switching memory unit 113, and a characteristic value memory unit 114.

[0071] The sensor control unit 101 is a functional unit that controls the operation of the light detection sensor 91. The sensor control unit 101 receives a synchronization signal that is output when the light detection sensor 91 detects laser light.

[0072] The light-emission control unit 102 is a functional unit that controls the on / off of the laser diode 21 (light-emitting element) and adjusts the amount of laser light emitted from the laser diode 21. Specifically, the light-emission control unit 102 transfers a turn-on signal and an off signal corresponding to image data to the laser diode 21 in response to a signal from a count unit 103 that counts up based on a synchronization signal received by the sensor control unit 101, in order to form an electrostatic latent image on the photosensitive drum 30. The timing at which this signal transfer starts is referred to as the above-mentioned write start timing. Note that although there are techniques for varying the amount of laser light at specific timings during laser light scanning, in this embodiment, in order to reduce manufacturing costs, the light-emission control unit 102 irradiates laser light at a constant amount throughout the entire laser light scanning period.

[0073] The count unit 103 is a functional unit that automatically increments an internal count value when the sensor control unit 101 receives a synchronization signal from the light detection sensor 91. Specifically, the count unit 103 resets its internal count value when the sensor control unit 101 starts receiving a synchronization signal. The count unit 103 then outputs a signal to the light emission control unit 102 when the incremented count value reaches a predetermined value. The predetermined value is determined by the sum of a reference value determined based on the arrangement of the photosensitive drum 30 and the arrangement of the light detection sensor 91 and a correction value for the misalignment in the scanning direction (main scanning misalignment) of each color. The correction value for the misalignment in the scanning direction (main scanning misalignment) is stored in a correction value storage unit 112, and the light emission control unit 102 reads the correction value from the correction value storage unit 112 before starting image formation by emitting laser light from the laser diode 21.

[0074] The deflection control unit 104 is a functional unit that controls the polygon motor 23a to rotate the polygon motor 23a, and causes the laser light emitted from the laser diode 21 to scan the photosensitive drum 30 in the main scanning direction.

[0075] The correction value calculation unit 105 is a functional unit that calculates correction values ​​by color misregistration correction. The correction value calculation unit 105 updates the correction values ​​stored in the correction value storage unit 112 with the calculated correction values. In this configuration, the correction values ​​calculated by color misregistration correction through color matching operation correct the deviation in the timing at which the laser light starts writing, allowing an electrostatic latent image to be formed at the targeted position on the photosensitive drum 30, thereby forming a high-quality image.

[0076] The gain switching unit 106 is a functional unit that switches the gain of the light detection sensor 91 by outputting a gain switching signal to the gain switching circuit 92 of the synchronization detection plate 90. When the gain is switched, the gain switching unit 106 stores information about the gain (for example, the value of the gain resistor or the level of the gain switching signal) in the gain switching memory unit 113.

[0077] 12(b) shows the operation when the laser light incident on the light detection sensor 91 becomes even stronger. If the laser light incident on the light detection sensor 91 becomes too strong, the laser light is detected at a timing when it should not be detected due to the influence of stray light, resulting in malfunction. In this case, the gain switching unit 106 reduces the gain of the light detection sensor 91 (for example, as shown in FIG. 12(a), by setting the gain switching signal SIG1 to a high level and the gain switching signal SIG2 to a low level), thereby lowering the voltage of the detection signal as shown in FIG. 12(b), and preventing the stray light from being detected.

[0078] On the other hand, Figure 13(b) shows the operation when the laser light incident on the light detection sensor 91 becomes even weaker. If the laser light incident on the light detection sensor 91 becomes too weak, the analog detection signal will not reach the constant voltage (threshold) of the comparator, and the laser light will fail to be detected, resulting in a malfunction. In this case, the gain switching unit 106 increases the gain of the light detection sensor 91 (for example, as shown in Figure 13(a), by setting the gain switching signal SIG1 to low level and the gain switching signal SIG2 to low level), thereby raising the voltage of the detection signal as shown in Figure 13(b), and making it possible to detect the laser light.

[0079] 10, when the gain of the light detection sensor 91 is switched, the graph of the amount of change in the write start timing also changes. In order to define such a graph of the amount of change in the write start timing, information on a characteristic value table or characteristic value curve (described later) corresponding to each gain is stored in the characteristic value storage unit 114. The correction value calculation unit 105 uses the information on the characteristic value table or characteristic value curve stored in the characteristic value storage unit 114 to calculate the amount of correction for the deviation in the write start timing for each gain.

[0080] Note that the deviation in the write start timing that is the target of correction by correction value calculation unit 105 is a minute deviation on the order of several tens of μm, and therefore, it is possible to ignore this minute deviation unless the operation requires highly accurate color matching, such as a printing operation. In this case, the normal usage of image forming apparatus 1 may be limited to operations that require highly accurate color matching, such as a printing operation, and only the information on the characteristic value table or characteristic value curve corresponding to the gain of light detection sensor 91 used in that limited operation may be stored in characteristic value storage unit 114. This makes it possible to minimize the memory area used by characteristic value storage unit 114 and prevent an increase in the cost of parts.

[0081] The characteristic value processing unit 107 is a functional unit that calculates the amount of change in the write start timing for each gain, estimates the curve of the write start timing, and updates the information of the characteristic value table or characteristic value curve stored in the characteristic value storage unit 114 according to the estimated curve. Hereinafter, the characteristic value table or characteristic curve may be collectively referred to as "characteristic value information."

[0082] FIG. 14(a) shows an example of a characteristic value table, which is information in a table format that associates the amount of laser light incident on the light detection sensor 91 with the amount of change in the write start timing corresponding to the laser diodes 21a and 21b. A characteristic value table is prepared for each laser light (color) having a different path. Note that a common characteristic value table may be used for laser light (color) having a common scanning direction. This reduces memory consumption. When the amount of laser light is determined by a density adjustment operation or the like of the image forming apparatus 1, the correction value calculation unit 105 calculates the amount of change in the write start timing corresponding to that amount of light according to the characteristic value table of FIG. 14(a), and calculates a correction value. For example, when the image forming apparatus 1 operates with the laser diode 21a's laser beam intensity set to 1.3 mW and the laser diode 21b's laser beam intensity set to 1.1 mW, the write start timing of the laser diode 21a is delayed by 8.640 ns, and the write start timing of the laser diode 21b is advanced by 2.526 ns. Using such a characteristic value table, the correction value calculation unit 105 can calculate the amount of change in the write start timing even when the light intensity of each laser diode 21 is changed. The correction value calculation unit 105 then corrects the calculated amount of change in the write start timing, thereby providing a high-quality image. The characteristic value table may be a table, as shown in FIG. 14(b), that associates the ratio (light intensity ratio) of the laser beam incident on the light detection sensor 91 to a reference light intensity with the amount of change in the write start timing corresponding to the laser diodes 21a and 21b.

[0083] Here, with reference to FIG. 15 , we will explain in detail how the characteristic value table is used in the image forming apparatus 1. Color misalignment in the image forming apparatus 1 is corrected during color matching. A color matching pattern is formed on the transfer belt 40 and detected by the density detector 45. To form the color matching pattern, the image forming apparatus 1 irradiates the laser beam with a specific light intensity. The write start timing is determined based on the output signal of the light detection sensor 91, and any changes in the laser beam intensity will result in a shift in the write start timing. When the color matching pattern is formed, the write start timing also shifts depending on the light intensity at that time. Since color matching is performed under this shift, the correction value calculated by the correction value calculation unit 105 during color matching includes a correction value for the change in the write start timing. Using FIG. 15 as an example, if the laser beam intensity of the laser diode 21a during color matching is 4.1 mW, the write start timing will shift by 32.542 ns. The correction value calculated during color matching is a correction value that corrects for this 32.542 ns shift. Therefore, if the laser beam intensity of the laser diode 21a during normal printing is the same, 4.1 mW, the write start timing will not change due to the change in the light intensity. On the other hand, if the laser beam intensity of the laser diode 21a during normal printing changes from 4.1 mW, the write start timing will also change from 32.542 ns.

[0084] Therefore, in this embodiment, when color matching is successfully completed, the control device 10 stores the light intensity of the laser beam as an operating condition for color matching, and corrects the write start timing to cancel (eliminate) the difference between the amount of change in the write start timing that occurs when operating at the light intensity during printing and the amount of change in the write start timing that occurs when operating at the light intensity during color matching. For example, in the example of Figure 15, if the light intensity of the laser beam from the laser diode 21a during color matching is 4.1 [mW] and the light intensity during printing is 3.8 [mW], the correction value calculation unit 105 corrects the write start timing of the laser diode 21a by calculating a correction value for 0.862 [ns], which is the difference in the amount of change in the write start timing corresponding to the two light intensities in the characteristic value table. Furthermore, if the light intensity of the laser light from the laser diode 21b during color matching is 4.2 [mW] and the light intensity during printing operation is 4.0 [mW], the correction value calculation unit 105 corrects the writing start timing of the laser diode 21b by calculating a correction value for -0.463 [ns], which is the difference between the change amounts of the writing start timing corresponding to the two light intensities in the characteristic value table.

[0085] 14 and 15, the write start timing is corrected using a characteristic value table as characteristic value information, but as shown in Fig. 16, the write start timing may be corrected using a polynomial characteristic value curve as characteristic value information. For example, from the plot of the amount of change in the write start timing shown in Fig. 14 (measurement results at several points), an approximation curve of a polynomial is calculated, and the coefficients a0 to a n (In FIG. 16, up to a6) are determined. Therefore, the control device 10 can calculate the amount of change in the write start timing using the laser light intensity LDp as an input value and the following equation (1). In addition, polynomial characteristic value curves are also prepared for each laser light (color) with a different path.

[0086] Change in write start timing = a n ×LDp n +an-1 ×LDp n-1 +···+a1×LDp+a0···(1)

[0087] When color matching is successfully completed, the control device 10 stores the laser light intensity as an operating condition for color matching, and corrects the write start timing to cancel (eliminate) the difference between the amount of change in write start timing that occurs when operating with the light intensity for printing and the amount of change in write start timing that occurs when operating with the light intensity for color matching. For example, assume that the coefficients of the characteristic value curve indicating the change in write start timing are a0 = 42.249, a1 = -62.972, a2 ​​= 24.779, a3 = -5.0273, a4 = 0.4872, a5 = -0.0151, and a6 = -0.0003. If the laser beam intensity of the laser diode 21a during color matching is 4.1 mW and the laser beam intensity of the laser diode 21a during printing is 3.8 mW, the change amounts of the write start timing in the characteristic value curve are calculated as −27.1360 ns and −26.3738 ns, respectively, using the above-described formula (1). The correction value calculation unit 105 corrects the write start timing of the laser diode 21a by correcting the difference between these two change amounts, −0.7622 ns. By calculating and correcting the write start timing in this manner, deviations in the write start timing that occur during printing can be suppressed, resulting in high-quality images. Furthermore, when storing the characteristic value curve as characteristic value information, only the coefficients of the polynomial need be stored, thereby reducing the consumption of storage space compared to a characteristic value table as specific value information.

[0088] Here, a method for determining the values ​​of the resistors R1 to R3 of the gain switching circuit 92 of the synchronization detection plate 90, which enables the characteristic value processing unit 107 to accurately estimate the curve of the amount of change in the write start timing, will be described. As described above, the sensitivity (gain) of the light detection sensor 91 is determined by the value of the gain resistor of the gain switching circuit 92. In this embodiment, for example, the gain resistor values ​​can be broadly divided into two, as shown in FIG. 17 . The first is the gain resistor value used only in the process of updating the information in the characteristic value table or characteristic value curve. The second is the gain resistor value used in both the normal usage of the image forming apparatus 1 and the update process. Since the gain resistor value used in the normal usage of the image forming apparatus 1 is the most important, a reference gain resistor value is first determined. Next, the maximum and minimum gain resistor values ​​are determined. To accurately estimate the curve of the amount of change in the write start timing within the range of the light intensity of the laser light incident on the light detection sensor 91, measurement results for the amount of change from one end of the light intensity range to the other are required. Furthermore, as described above, the magnitude of the detection signal voltage of the light detection sensor 91 is proportional to the product of the incident laser light intensity P and the gain resistor value G. Therefore, to obtain a measurement result of the amount of change in the incident laser light intensity range from one end to the other, the ratio of the gain resistor values ​​must be changed according to the number of light intensity ratios. Therefore, in this embodiment, the gain resistor values ​​are determined as follows. Let Ptyp be the median light intensity of the laser light, Pmax be the maximum light intensity, and Pmin be the minimum light intensity. The maximum gain resistor value is selected so as to be close to the value obtained by multiplying the reference gain resistor value by the light intensity ratio Pmax / Ptyp. The minimum gain resistor value is selected so as to be close to the value obtained by multiplying the reference gain resistor value by the light intensity ratio Pmin / Ptyp. By selecting resistors R1 to R3 to form these gain resistor values, the curve of the amount of change in the write start timing can be estimated with high accuracy throughout the entire range of laser light intensity used in the image forming apparatus 1.

[0089] For example, let's say the reference gain resistance value is 2.31 kΩ. If Pmax / Ptyp=1.3 (+30%) and Pmin / Ptyp=0.69 (-30%), then the maximum gain resistance value is 2.31 kΩ × 1.3 = 3.00 kΩ, and the minimum gain resistance value is 2.31 kΩ × 0.69 = 1.59 kΩ. By switching the gain switching signal for the gain switching circuit 92 ON / OFF, the values ​​of resistors R1, R2, and R3 that can be set to values ​​close to the three types of gain resistance values ​​(2.31 kΩ, 3.00 kΩ, and 1.59 kΩ) are 3.0 kΩ, 10.0 kΩ, and 5.1 kΩ, respectively.

[0090] Furthermore, the value of the gain resistor switched in the characteristic value update process described below includes a value equal to or greater than the value obtained by multiplying the ratio of the maximum light amount to the reference light amount, where the light amount of the laser light used in the printing operation is the reference light amount, by the value of the gain resistor switched in the printing operation.Furthermore, the value of the gain resistor switched in the characteristic value update process described below includes a value equal to or less than the value obtained by multiplying the ratio of the minimum light amount to the reference light amount, where the light amount of the laser light used in the printing operation is the reference light amount, by the value of the gain resistor switched in the printing operation.

[0091] Finally, consider whether gain switching is necessary during normal use of the image forming apparatus 1. If gain switching is necessary, select a usable gain resistor value from among those that can be set as the gain of the light detection sensor 91 when resistors R1, R2, and R3 are set to the above values. If no usable value is available, resistors R1, R2, and R3 alone are insufficient. Therefore, add a circuit to the gain switching circuit 92 and add a new gain switching signal to enable setting the gain resistor value used in the image forming apparatus 1. By configuring the gain switching circuit 92 for the light detection sensor 91 in this manner, the characteristic value information update process by the characteristic value processing unit 107 can accurately estimate the curve of the change in the write start timing. This suppresses deviations in the write start timing that occur during printing operations, enabling the provision of high-quality images.

[0092] It is not necessary to separate the gain switching signal used when updating the characteristic value information by the characteristic value processing unit 107 from the gain switching signal used in the normal usage of the image forming apparatus 1. Since the gain (sensitivity) changes depending on the combination of gain switching signals, it is sufficient to select the gain to be used in the normal usage of the image forming apparatus 1 from among those combinations.

[0093] The reference value storage unit 111 is a functional unit that stores the above-mentioned reference values ​​and is realized by, for example, the above-mentioned ROM.

[0094] The correction value storage unit 112 is a functional unit that stores the correction values ​​calculated by the correction value calculation unit 105. The correction value storage unit 112 is realized by, for example, the above-mentioned ROM or RAM.

[0095] The gain switching storage unit 113 is a functional unit that stores information about the gain switched by the gain switching unit 106. The gain switching storage unit 113 is realized by, for example, the above-mentioned ROM or RAM.

[0096] The characteristic value storage unit 114 is a functional unit that stores information on a characteristic value table or a characteristic value curve. When the characteristic value processing unit 107 estimates a curve for the write start timing, the information on the characteristic value table or the characteristic value curve in the characteristic value storage unit 114 is updated.

[0097] The above-mentioned sensor control unit 101, light emission control unit 102, counting unit 103, deflection control unit 104, correction value calculation unit 105, gain switching unit 106, and characteristic value processing unit 107 are realized by the above-mentioned CPU executing a program. Note that at least some of the sensor control unit 101, light emission control unit 102, counting unit 103, deflection control unit 104, correction value calculation unit 105, gain switching unit 106, and characteristic value processing unit 107 may be realized by a hardware circuit such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit).

[0098] Note that the functional units of the control device 10 shown in Fig. 11 are conceptually shown, and are not limited to such a configuration. That is, the functional units of the control device 10 do not need to be configured as clear software modules as the blocks shown in Fig. 11, but rather the functions of the functional units as a whole may be realized by executing a program on the control device 10. For example, multiple functional units illustrated as independent functional units in the control device 10 shown in Fig. 11 may be configured as a single functional unit. On the other hand, the function of one functional unit in the control device 10 shown in Fig. 11 may be divided into multiple functional units and configured as multiple functional units.

[0099] (Regarding characteristic value update processing for image forming devices) FIG. 18 is a diagram illustrating an outline of the operation of the characteristic value update process of the image forming apparatus according to the embodiment. FIG. 19 is a flowchart showing an example of the flow of the characteristic value update process of the image forming apparatus according to the embodiment. FIG. 20 is a diagram illustrating the operation of estimating a curve of the amount of change in the write start timing from measurement results in the image forming apparatus according to the embodiment. FIG. 21 is a diagram illustrating the operation of estimating a curve (second) of the amount of change in the write start timing from measurement results in the image forming apparatus according to the embodiment. FIG. 22 is a diagram illustrating updating of the characteristic value table in the image forming apparatus according to the embodiment. FIG. 23 is a diagram illustrating updating of the characteristic value curve in the image forming apparatus according to the embodiment. The characteristic value update process of the image forming apparatus 1 according to the present embodiment will be described with reference to FIGS. 18 to 23.

[0100] As shown in FIGS. 14 to 16 , the image forming apparatus 1 according to this embodiment corrects the write start timing using characteristic value information (characteristic value table or characteristic value curve) indicating the amount of change in the write start timing. However, if the amount of change in the write start timing of the optical writing device 20 does not match the correction amount of the write start timing calculated from the characteristic value information, the deviation cannot be properly corrected. For example, if the spot diameter of the laser light incident on the light detection sensor 91 is not narrowed, the spot diameter will vary significantly for each optical writing device 20. As a result, the amount of change in the write start timing when the amount of laser light changes will vary significantly for each optical writing device 20. This may result in a situation where characteristic value information that can calculate an appropriate correction amount for one optical writing device 20 does not calculate an appropriate correction amount for another optical writing device 20. Therefore, in this embodiment, the characteristic value information is updated to match the characteristics of the optical writing device 20 (the curve of the estimated amount of change in the write start timing). The update operation will be described below.

[0101] For example, when a user of the image forming apparatus 1 requests execution of a process for updating characteristic value information, the image forming apparatus 1 starts executing the characteristic value update process. As a result, as shown in FIG. 18 , the characteristic value information (characteristic value table or characteristic value curve) is updated to match the characteristics (curve of the estimated change in the writing start timing) of each optical writing device 20. By calculating the correction amount of the writing start timing using the updated characteristic value information, it is possible to suppress the variation in the characteristics of each optical writing device 20 and provide high-quality images. In this case, when updating the characteristic value table as characteristic value information, the image forming apparatus 1 updates the change amount associated with each light amount. Furthermore, when updating the characteristic value curve as characteristic value information, the image forming apparatus 1 updates the coefficients of each term in the polynomial of the characteristic value curve. Furthermore, the different characteristics (curve of the change in the writing start timing) of each optical writing device 20 may vary due to, for example, the influence of the spot diameter of the laser light, as described above. This is a physical characteristic of the optical writing device 20 that is not easily affected by time, and therefore, by performing the characteristic value update process just once immediately after assembling the image forming apparatus 1 or when replacing the optical writing device 20 of the image forming apparatus 1, it is possible to obtain good characteristic value information tailored to the optical writing device 20 and correct the writing start timing with high precision. Alternatively, the control device 10 may detect whether the optical writing device 20 has been replaced, and if it detects that the optical writing device 20 has been replaced, it may automatically perform the characteristic value update process just once. A specific flow of the characteristic value update process will be described below with reference to FIGS. 19 to 23.

[0102] <Step S11> The gain switching unit 106 of the control device 10 switches to a specific gain for the light detection sensor 91. Then, the process proceeds to step S12.

[0103] <Step S12> The control device 10 executes pre-processing for detecting a change amount calculation pattern, which will be described later, and then proceeds to step S13.

[0104] <Step S13> The control device 10 causes the optical writing device 20 to form a change amount calculation pattern (first pattern) which is a pattern for calculating the change amount of the write start timing.

[0105] Here, the change amount calculation pattern refers to a pattern that can detect deviation in the main scanning direction. For example, it is composed of a pattern that combines patterns with different angles, such as a horizontal line pattern and a diagonal line pattern. In this embodiment, the change amount calculation pattern is a pattern that has the same shape as the pattern used in the color matching operation of the image forming device. In this case, the same shape means that the angle, length, width, and formation interval are all the same as the color matching pattern. Also, the change amount calculation pattern may be formed with the same density as the color matching pattern. This reduces the impact of differences in shape from the color matching pattern on the calculation results of the change amount in the writing start timing, enabling highly accurate estimation of the characteristics of the optical writing device 20 (the curve of the change amount in the writing start timing).

[0106] Furthermore, the control device 10 may form the change amount calculation pattern using only the laser diode 21 that irradiates the laser light incident on the light detection sensor 91. For example, in this embodiment, the change amount calculation pattern may be two colors, black and yellow. Because the laser light incident on the light detection sensor 91 is used for the image colors of black and yellow, the pattern may be formed using only these two colors. Therefore, the colors of the laser diode 21 are not limited to black and yellow. This makes it possible to minimize toner consumption.

[0107] Then, the process proceeds to step S14.

[0108] <Step S14> The control device 10 causes the concentration detector 45 to detect the toner concentration of the formed change amount calculation pattern, and acquires position information of the change amount calculation pattern, and then proceeds to step S15.

[0109] <Step S15> The control device 10 determines whether or not the detection of the change amount calculation pattern has been successful. If successful (step S15: Yes), the process proceeds to step S16, and if unsuccessful (step S15: No), the process proceeds to step S17.

[0110] <Step S16> The characteristic value processing unit 107 of the control device 10 calculates the amount of change in the write start timing from the position information of the acquired amount of change calculation pattern, and then the process proceeds to step S17.

[0111] <Step S17> The control device 10 checks whether the amount of change has been calculated for all switchable gains for the gain switching circuit 92. If the amount of change has been calculated for all gains (step S17: Yes), the process proceeds to step S18, and if not (step S17: No), the process returns to step S11. Note that the calculation of the amount of change is not limited to being performed for all switchable gains, and may be performed for some of the switchable gains.

[0112] <Step S18> By repeating the above-described processing of steps S11 to S17, calculation results of the amount of change for each gain in the light detection sensor 91 are obtained. Based on these calculation results, the characteristic value processing unit 107 calculates values ​​to be stored in the characteristic value table or coefficients in the characteristic value curve. Note that the gains switched by the gain switching unit 106 in step S11 of the repeated processing of steps S11 to S17 above include gains switched during printing operations.

[0113] Here, with reference to FIG. 20, the operation of calculating the values ​​to be stored in the characteristic value table will be specifically described. By repeating the above-described steps S11 to S17, the results of the amount of change in the write start timing for each gain resistance value are obtained based on the amount of laser light when the change amount calculation pattern is formed. Because the amount of laser light when the change amount calculation pattern is formed is not changed midway, the calculation results spread along the vertical axis as shown in FIG. 20. This spread occurs due to differences in the gain resistance values. To estimate the curve of the amount of change in the write start timing from these calculation results, the calculation results must be re-plotted. When a certain gain resistance value (reference sensitivity) is fixed, the amount of change in the write start timing when the amount of laser light incident on the light detection sensor 91 is changed is expressed as a curve. In this embodiment, the calculation results are re-plotted as follows: For each calculation result, the characteristic value processing unit 107 calculates the ratio of the gain resistance values ​​obtained by dividing the gain resistance value corresponding to each calculation result by a certain gain resistance value. The characteristic value processing unit 107 then multiplies the amount of laser light when the change amount calculation pattern is formed by the calculated ratio of the gain resistance value, thereby converting it into an amount of laser light. This makes it possible to estimate a curve of the amount of change in the write start timing when a certain gain resistance value is fixed. Here, the certain gain resistance value refers to the gain resistance value used in the normal usage of the image forming apparatus 1 (e.g., the gain resistance value used during printing). The characteristic value processing unit 107 fixes the gain resistance value used in the normal usage of the image forming apparatus 1 and multiplies the amount of laser light when the change amount calculation pattern is formed by the ratio of the gain resistance value, thereby converting it into an amount of laser light, thereby making it possible to estimate a curve of the amount of change in the write start timing for the gain resistance value used in the normal usage of the image forming apparatus 1. This makes it possible for the characteristic value processing unit 107 to calculate the amount of change corresponding to each amount of light in the characteristic value table from the estimated curve of the amount of change in the write start timing, as shown in FIG. 20 .

[0114] Furthermore, when the gain of the light detection sensor 91 is switched during normal operation of the image forming apparatus 1, for example, during an adjustment operation or printing operation, there will be two or more curves of the amount of change in the write start timing to be estimated. This estimation operation will be described with reference to FIG. 21. The method for estimating the curve of the amount of change in the write start timing in this case is the same as when a single gain resistor value is used during normal operation of the image forming apparatus 1. That is, the characteristic value processing unit 107 replaces the fixed gain resistor value with each gain resistor value used during normal operation of the image forming apparatus 1 and calculates the ratio of the gain resistor values. The characteristic value processing unit 107 then multiplies the amount of laser light used to form the change amount calculation pattern by the calculated ratio of the gain resistor values ​​to convert it into the amount of laser light, thereby estimating the curve of the amount of change in the write start timing corresponding to each gain in the characteristic value table. As a result, as shown in FIG. 21, the characteristic value processing unit 107 can calculate the amount of change corresponding to each light amount in the characteristic value table corresponding to each gain from the estimated curve of the amount of change in the write start timing corresponding to each gain.

[0115] Here, as explained in FIGS. 20 and 21, if the amount of misalignment is calculated by switching to a gain resistance value corresponding to all light intensities in the characteristic value table, the number of calculation points becomes enormous, resulting in an increase in processing time. Furthermore, an enormous number of calculation points complicates the gain switching circuit 92, resulting in increased costs. Therefore, the control device 10 may repeat the above-described steps S11 to S17 with a number of calculation points that is fewer than the number of columns in the characteristic value table. In this case, as shown in FIG. 22, the control device 10 estimates the characteristics of the optical writing device 20 (the curve of the amount of change in the writing start timing) by performing an interpolation process in accordance with the number of columns in the characteristic value table from a plot showing calculation results that are fewer than the number of columns in the characteristic value table. This allows the value (amount of change) required to update the characteristic value table accurately to be calculated in a short time.

[0116] When calculating values ​​to update the characteristic value table, the characteristic value processing unit 107 may use the amount of change in the write start timing corresponding to one calculation result as a reference value and calculate the difference from the reference value. This calculation makes it possible to keep the values ​​updated in the characteristic value table at a certain level, preventing overflow of the updated values ​​and reducing memory consumption.

[0117] Furthermore, as described above, the number of calculation points for estimating the curve of the amount of change in the write start timing may be, for example, three or four. That is, the above-described repeated process is performed while switching between three or four gains by the gain switching unit 106. As shown in FIGS. 20 and 21 above, the characteristics of the optical writing device 20 (the curve of the amount of change in the write start timing) have a nonlinear shape. In this case, in order to minimize the number of calculation points and perform interpolation with high accuracy, at least three calculation results are required. However, the number of gain switchings by the gain switching circuit 92 is two. n (n: number of gain switching signals) and if you try to calculate with three or more points, the minimum is 2 2 = 4 possible calculations. Therefore, the minimum score is 3 or 4 points.

[0118] The above-mentioned interpolation process is performed by, for example, linear interpolation, which allows for accurate correction of deviations and provides high-quality images.

[0119] Next, with reference to Fig. 23, the operation of calculating the coefficients of the polynomial of the characteristic value curve will be specifically described. The control device 10 repeats the above-mentioned steps S11 to S17 with the number of calculation points N+1, which is larger than the order N (N≧2) of the polynomial, based on the light intensity of the laser beam when the change amount calculation pattern is formed. That is, the above-mentioned repeats are performed while the gain switching unit 106 switches to the gain N+1. In this case, the method of finding the calculation points is the same as the method described above with reference to Figs. 20 and 21. Then, the characteristic value processing unit 107 calculates the coefficients a of each order of the approximation equation for the plot of the calculation result N+1.n ∼a0 is calculated. This allows the characteristic value processing unit 107 to accurately approximate the characteristic of the optical writing device 20 (the curve of the amount of change in the writing start timing) in a short time.

[0120] The order N of the approximation formula that approximates the characteristic of the optical writing device 20 (the curve of the amount of change in the write start timing) may be set to 3 or 4. This is because if the order of the approximation formula is set to 5 or more, there is a risk that distortion of the interpolation curve will become large locally between calculation points. Therefore, by setting the order N of the approximation formula to 3 or 4, it is possible to accurately obtain an approximation curve of the characteristic value curve while reducing the number of calculation points.

[0121] In the following description, the values ​​stored in the characteristic value table (amount of change relative to the amount of light) and the coefficients of the polynomial of the characteristic value curve may be referred to as "characteristic values."

[0122] The description will be continued by returning to Fig. 19. After the process of step S18, the process proceeds to step S19.

[0123] <Step S19> The characteristic value processing unit 107 determines whether the calculated characteristic value can be updated to the characteristic value information. If the characteristic value can be updated (step S19: Yes), the process proceeds to step S20. If the characteristic value cannot be updated (step S19: No), the characteristic value update process ends.

[0124] <Step S20> The characteristic value processing unit 107 updates the characteristic values ​​of the characteristic value information calculated by estimating a curve of the amount of change in the write start timing to the characteristic value storage unit 114. Specifically, when the characteristic value information is a characteristic value table, the characteristic value processing unit 107 updates the amount of change corresponding to each amount of light in the characteristic value table as the characteristic value, and when the characteristic value information is a characteristic value curve, the characteristic value processing unit 107 updates the coefficients of the polynomial of the characteristic value curve as the characteristic value.

[0125] Note that, based on the calculation results, the characteristic values ​​of the characteristic value information may be updated to correspond to each value of gain resistance used in normal usage of the image forming apparatus 1. However, this may increase the processing load and the capacity load of the characteristic value storage unit 114. To avoid this, the estimated curve of the change amount of the write start timing may be one corresponding to a specific gain resistance, and the characteristic value processing unit 107 may update the characteristic value of the characteristic value information corresponding to this one curve in the characteristic value storage unit 114. When there are multiple values ​​of gain resistance used in normal usage of the image forming apparatus 1, the correction value calculation unit 105 may calculate the change amount of the write start timing for the gain to be used using one curve of the change amount of the write start timing estimated by the characteristic value processing unit 107 (i.e., the characteristic value information) and the ratio between the gain resistance to be used and the value of the specific gain resistance, and calculate the characteristic value corresponding to this change amount.

[0126] Furthermore, the value of the gain resistor is not limited to a predetermined value, and a previously measured value may be stored in memory (for example, the characteristic value storage unit 114). When performing characteristic value update processing for the characteristic value table or characteristic value curve, or when correcting the write start timing using the updated characteristic value table or characteristic value curve, the value of the gain resistor (actually measured value) stored in memory may be read out and the respective processing may be performed. This allows the curve of the amount of change in the write start timing to be estimated with high accuracy without being affected by component variations, suppressing deviations in the write start timing that occur during printing operations and providing high-quality images.

[0127] When the characteristic value update process described above is completed, the control device 10 may notify the image forming apparatus 1 that the characteristic value update process has been completed so that the characteristic value update process will not be executed the next time the image forming apparatus 1 is started. In this case, the notification method may include displaying the information on a display provided in the image forming apparatus 1 or sending an email to a predetermined address that has been set in advance.

[0128] (Flow of color matching operation of image forming device) 24 is a flowchart showing an example of the flow of the color matching operation of the image forming apparatus 1 according to this embodiment. The flow of the color matching operation of the image forming apparatus 1 according to this embodiment will be described with reference to FIG.

[0129] <Step S31> The gain switching unit 106 of the control device 10 switches the gain of the light detection sensor 91 in accordance with the amount of laser light from the laser diode 21 used in the color matching operation, and then the process proceeds to step S32.

[0130] <Step S32> The control device 10 executes pre-detection processing, and then proceeds to step S33.

[0131] <Step S33> The control device 10 forms a color matching pattern (second pattern) for color matching. In this embodiment, when forming the color matching pattern, the function of calculating the correction value using the characteristic value information described above is disabled. Then, the process proceeds to step S34.

[0132] <Step S34> The control device 10 causes the density detector 45 to detect the toner density of the formed color matching pattern.

[0133] It goes without saying that the laser diode 21 that forms the color matching pattern and the concentration detector 45 that detects the toner concentration of the color matching pattern are the same as the laser diode 21 that forms the change amount calculation pattern in the characteristic value update process described above and the concentration detector 45 that detects the toner concentration of the change amount calculation pattern, respectively.

[0134] Then, the process proceeds to step S35.

[0135] <Step S35> The control device 10 determines whether or not the detection of the color matching pattern was successful. If the detection was successful (step S35: Yes), the process proceeds to step S36, and if the detection was not successful (step S35: No), the color matching operation is terminated.

[0136] <Step S36> The correction value calculation unit 105 of the control device 10 calculates a correction value using the result of detecting the color matching pattern. In this case, even when the color matching pattern is formed, the writing start timing is shifted depending on the amount of light at that time, but since color matching is performed in this shifted state, the correction value calculated by the correction value calculation unit 105 for color matching includes a correction value for the amount of change in the writing start timing. Then, the process proceeds to step S37.

[0137] <Step S37> The control device 10 determines whether the correction value calculated by the correction value calculation unit 105 is a normal value. If the correction value is a normal value (step S37: Yes), the process proceeds to step S38, and if the correction value is not a normal value (step S37: No), the color matching operation ends.

[0138] <Step S38> The correction value calculation unit 105 stores or updates the calculated correction value in the correction value storage unit 112. Then, the process proceeds to step S39.

[0139] <Step S39> If the color matching is completed normally, the control device 10 stores or updates the light amount and gain of the laser light when the color matching pattern was formed, and then ends the color matching operation.

[0140] (Flow of printing operation of image forming device) 25 is a flowchart showing an example of the flow of the printing operation of the image forming apparatus 1 according to the embodiment, The flow of the printing operation of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG.

[0141] <Step S51> The gain switching unit 106 of the control device 10 switches the gain of the light detection sensor 91 in accordance with the amount of laser light from the laser diode 21 used in the printing operation of the image forming apparatus 1. Then, the process proceeds to step S52.

[0142] <Step S52> The control device 10 executes pre-processing for the printing operation, and then proceeds to step S53.

[0143] <Step S53> The light emission control unit 102 of the control device 10 reads out the gain information stored in the gain switching memory unit 113, switches the gain of the light detection sensor 91 so that the laser light is detected at that gain, and then initializes the laser diode 21. Then, the process proceeds to step S54.

[0144] <Step S54> If the initialization of the laser diode 21 has been performed normally (step S54: Yes), the process proceeds to step S55, and if the initialization has not been performed normally (step S54: No), the process proceeds to step S61.

[0145] <Step S55> The sensor control unit 101 detects laser light by the light detection sensor 91 and checks whether or not a synchronization signal has been received from the light detection sensor 91. If a synchronization signal has been received (step S55: Yes), the process proceeds to step S56, and if not (step S55: No), the process proceeds to step S61.

[0146] <Step S56> The control device 10 reads out the color matching execution conditions. Specifically, the control device 10 reads out the gain information stored in the above-mentioned color matching operation. Then, the process proceeds to step S57.

[0147] <Step S57> When the amount of laser light during printing operation changes from the amount of laser light during color matching operation, the write start timing shifts depending on the characteristics of the optical writing device 20 (the curve of the amount of change in the write start timing), so the correction value calculation unit 105 of the control device 10 uses a characteristic value table or characteristic value curve to calculate a correction value for correcting the shift in the write start timing, thereby adjusting the write start timing.

[0148] In addition, when forming a high-quality image or pattern in which the influence of the characteristics of the optical writing device 20 (the curve of the amount of change in the writing start timing) cannot be ignored, the function of calculating the correction value using the above-mentioned characteristic value information can be enabled and operated.

[0149] Then, the process proceeds to step S58.

[0150] <Step S58> The control device 10 executes the printing process, and then proceeds to step S59.

[0151] <Step S59> If all print jobs have been completed (step S59: Yes), the process proceeds to step S60, and if not (step S59: No), the process returns to step S56.

[0152] <Step S60> The control device 10 executes post-printing processing and then ends the printing operation.

[0153] <Step S61> The control device 10 executes a forced print termination process to terminate the printing operation, and then terminates the printing operation.

[0154] As described above, in the image forming apparatus 1 according to this embodiment, the laser diode 21 emits a laser beam, the polygon mirror 23 deflects the laser beam emitted from the laser diode 21 to scan the photosensitive drum 30, the light detection sensor 91 detects the laser beam in order to determine a write start timing for forming a latent image by scanning the laser beam emitted from the laser diode 21 onto the photosensitive drum 30 via the polygon mirror 23, the gain switching circuit 92 switches the light detection sensor 91 to one of a plurality of gains for detecting the laser beam, and the control device 10 controls the operation of the image forming apparatus 1, an emission control unit 102 controls the amount of light emitted by the laser diode 21, a gain switching unit 106 switches the gain via a gain switching circuit 92 according to the set amount of light, a correction value calculation unit 105 corrects a deviation in the write start timing using characteristic value information indicating the relationship between the amount of light and the amount of change in the write start timing, and a characteristic value processing unit 107 calculates the amount of change in the write start timing while being switched to each gain by the gain switching unit 106 and updates the characteristic values ​​constituting the characteristic value information based on the amount of change. This makes it possible to appropriately correct a deviation in the write start timing when the gain is switched and correct the deviation using a correction value corresponding to the image forming apparatus 1, while also reducing costs.

[0155] In the above-described embodiment, when at least one of the functional units of the control device 10 of the image forming apparatus 1 is realized by executing a program, the program is provided by being pre-installed in a ROM or the like. In the above-described embodiment, the program executed by the control device 10 of the image forming apparatus 1 may be provided by being recorded in an installable or executable file format on a computer-readable recording medium such as a CD-ROM (Compact Disc Read Only Memory), a flexible disk (FD), a CD-R (Compact Disk-Recordable), or a DVD (Digital Versatile Disc). In the above-described embodiment, the program executed by the control device 10 of the image forming apparatus 1 may be stored on a computer connected to a network such as the Internet and provided by being downloaded via the network. In the above-described embodiment, the program executed by the control device 10 of the image forming apparatus 1 may be provided or distributed via a network such as the Internet. In the above-described embodiment, the program executed by the control device 10 of the image forming apparatus 1 has a modular configuration including at least one of the above-described functional units. In actual hardware, the CPU reads and executes the program from the above-described storage device, thereby loading and generating the above-described functional units into a main storage device.

[0156] The aspects of the present invention are as follows. <1> An image forming apparatus, A light emitting element that emits light; a deflector that deflects the light emitted from the light-emitting element and causes the light to scan on a photosensitive member; a light detecting element that detects light emitted from the light emitting element in order to determine a writing start timing for forming a latent image by scanning the light onto the photosensitive member via the deflector; a sensitivity switching circuit for switching the sensitivity of the light detection element to one of a plurality of sensitivities for detecting the light; a control unit that controls the operation of the image forming apparatus; Equipped with The control unit a light emission control unit that controls the amount of light emitted by the light emitting element; a sensitivity switching unit that switches the sensitivity via the sensitivity switching circuit in accordance with the set light amount; a correction unit that corrects the deviation of the writing start timing using characteristic value information that indicates the relationship between the amount of light and the amount of change in the writing start timing; an update unit that calculates a change amount of the write start timing while the sensitivity is switched to each of the sensitivities by the sensitivity switching unit, and updates the characteristic values ​​that constitute the characteristic value information based on the change amount; The image forming apparatus has the above. <2> the sensitivity switching unit switches to one of a plurality of sensitivities, the control unit forms a first pattern for calculating a change amount of the write start timing; a detection unit that detects the density of the first pattern, the update unit calculates a change amount of the writing start timing based on the concentration detected by the detection unit; while switching between different sensitivities by the sensitivity switching unit, a process of forming the first pattern by the control unit, a process of detecting the density of the first pattern by the detection unit, and a process of calculating the amount of change in the writing start timing by the update unit are repeated; The update unit When one of the plurality of sensitivities is set as a reference sensitivity, the sensitivity corresponding to each of the calculation operations in the repetitive processing is divided by the reference sensitivity to calculate a ratio; converting the amount of light from the light emitting element when the first pattern is formed into an amount of light corresponding to the amount of change in each of the calculation operations by multiplying the amount of light by each of the ratios, and updating the characteristic values ​​constituting the characteristic value information based on the amount of light and the amount of change; <1> 2. The image forming apparatus according to claim 1, wherein: <3> the correction unit calculates a correction value that eliminates a difference between a change in the writing start timing that occurs when the light emitting element is operated with a light amount during a printing operation and a change in the writing start timing that occurs when the light emitting element is operated with a light amount during color matching for correcting color misalignment between a plurality of colors. <2> 2. The image forming apparatus according to claim 1, wherein: <4> The light-emitting element when forming the first pattern and the detection unit that detects the density of the first pattern are the same as the light-emitting element when forming the second pattern used in the color matching and the detection unit that detects the density of the second pattern, respectively. <3> 2. The image forming apparatus according to claim 1, wherein: <5> The first pattern and the second pattern have the same angle, length, width and forming interval. <4> 2. The image forming apparatus according to claim 1, wherein: <6> The first pattern and the second pattern are formed with the same concentration. <4> 2. The image forming apparatus according to claim 1, wherein: <7> the control unit forms the first pattern using only the light emitting element that irradiates the light incident on the light detecting element. <2> ~ <6> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <8> The sensitivity that is switched by the sensitivity switching unit during the repeating process includes the sensitivity that is switched by the sensitivity switching unit during a printing operation. <2> ~ <7> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <9> The sensitivity switched by the sensitivity switching unit in the repeating process includes a sensitivity equal to or greater than a value obtained by multiplying a ratio of a maximum light amount to a reference light amount when the light amount of the light emitted from the light emitting element used during a printing operation is the reference light amount by the sensitivity switched by the sensitivity switching unit during the printing operation. <2> ~ <8> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <10> The sensitivity switched by the sensitivity switching unit in the repeated process includes a sensitivity equal to or less than a value obtained by multiplying a ratio of a minimum light amount to a reference light amount when the light amount of the light emitted from the light emitting element used during a printing operation is the reference light amount by the sensitivity switched by the sensitivity switching unit during the printing operation. <2> ~ <9> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <11> further comprising a storage unit that stores the characteristic value information; The characteristic value information stored in the storage unit is configured with characteristic values ​​corresponding to sensitivities switched by the sensitivity switching unit during a printing operation. <1> ~ <10> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <12> the updating unit updates the characteristic values ​​constituting the characteristic value information indicating a relationship between the amount of light and the amount of change for a specific sensitivity among the plurality of sensitivities; the correction unit calculates a change amount of the write start timing at the sensitivity to be used by using the characteristic value information corresponding to the specific sensitivity and a ratio between the sensitivity to be used and the specific sensitivity, and calculates a correction value corresponding to the change amount. <1> ~ <11> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <13> the characteristic value information is information in a table format that associates the light amount with the amount of change in the writing start timing; the updating unit updates the characteristic values ​​constituting the characteristic value information by interpolation processing on a plot determined by the amount of change in the writing start timing calculated in the repetitive processing and the amount of light converted corresponding to the amount of change. <2> ~ <10> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <14> The repeating process is executed while the sensitivity is switched to three or four sensitivity levels by the sensitivity switching unit. <13> 2. The image forming apparatus according to claim 1, wherein: <15> The interpolation process is a linear interpolation process. <13> or <14> 2. The image forming apparatus according to claim 1, wherein: <16> the characteristic value information is a characteristic value curve expressed by an N-th degree polynomial that indicates the relationship between the amount of light and the amount of change in the writing start timing, the updating unit calculates coefficients of respective orders of an approximation equation for a plot determined by the amount of change in the writing start timing calculated in the repetitive processing and the amount of light converted corresponding to the amount of change, and updates the coefficients as the characteristic values ​​of the characteristic value curve. <2> ~ <10> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <17> The repeated processing is executed while the sensitivity switching unit switches between N+1 sensitivities. <16> 2. The image forming apparatus according to claim 1, wherein: <18> The characteristic value curve is expressed by a third or fourth degree polynomial. <16> or <17> 2. The image forming apparatus according to claim 1, wherein: <19> During a printing operation, an operation of calculating a correction value by the correction unit using the characteristic value information is enabled; During the color matching, the operation of calculating the correction value by the correction unit using the characteristic value information is disabled. <3> ~ <6> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <20> the light emission control unit controls the amount of light emitted from the light emitting element to be constant throughout the entire period when the light is scanned over the photosensitive member. <1> ~ <19> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <21> The light detection element detects light emitted from the plurality of light emitting elements. <1> ~ <20> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <22> The photodetector element has a slit for restricting the direction of incidence of light. <1> ~ <21> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <23> The plurality of sensitivities switched by the sensitivity switching unit are stored in a storage unit as values ​​actually measured in advance. <1> ~ <22> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <24> the sensitivity switching circuit includes a resistor connected to the light detection element, and a switching element that switches whether or not to energize the resistor in response to a signal from the sensitivity switching unit. <1> ~ <23> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <25> an optical writing device including the light emitting element, the deflector, and the light detecting element; The control unit detects whether the optical writing device has been replaced, When the control unit detects that the optical writing device has been replaced, the update unit calculates a change amount of the writing start timing while the sensitivity switching unit switches to each of the sensitivities, and performs an operation of updating the characteristic values ​​constituting the characteristic value information based on the change amount. <1> ~ <24> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <26> When the characteristic value of the characteristic value information is updated by the update unit, the control unit notifies the update unit that the characteristic value has been updated. <1> ~ <25> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. [Explanation of symbols]

[0157] 1. Image forming device 2 Upper device 10 Control device 20 Optical writing device 21, 21a, 21b Laser diode 22a, 22b lenses 23 Polygon Mirror 23a Polygon motor 24a, 24b fθ lenses 25a, 25b mirrors 26a, 26b lenses 30, 30a to 30d Photosensitive drum 31, 31a to 31d Cleaning unit 32, 32a to 32d charging device 33, 33a to 33d developing roller 34, 34a to 34d Toner cartridges 40 Transfer belt 42 Transfer roller 45 Concentration detector 46, 46a~46d Home position sensor 50 Fuser roller 54 Paper feed roller 56 Registration roller pair 58 Paper ejection roller 60 Paper tray 70 Output tray 80 Communication control device 90, 90a, 90b Synchronous detection plate 91 Light detection sensor 91a lens 91b Light receiving part 92 Gain switching circuit 101 Sensor control unit 102 Light emission control unit 103 Counting section 104 Deflection control section 105 Correction value calculation unit 106 Gain switching section 107 Characteristic value processing section 111 Reference value storage unit 112 Correction value storage unit 113 Gain switching memory unit 114 Characteristic value storage unit R1, R2, R3 resistance SW1, SW2 switching elements [Prior art documents] [Patent documents]

[0158] [Patent Document 1] Patent Publication No. 2021-186974 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-303807 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-121770

Claims

1. An image forming apparatus, A light emitting element that emits light; a deflector that deflects the light emitted from the light-emitting element and causes the light to scan on a photosensitive member; a light detecting element that detects light emitted from the light emitting element in order to determine a writing start timing for forming a latent image by scanning the light onto the photosensitive member via the deflector; a sensitivity switching circuit for switching the sensitivity of the light detection element to one of a plurality of sensitivities for detecting the light; a control unit that controls the operation of the image forming apparatus; Equipped with The control unit a light emission control unit that controls the amount of light emitted by the light emitting element; a sensitivity switching unit that switches the sensitivity via the sensitivity switching circuit in accordance with the set light amount; a correction unit that corrects the deviation of the writing start timing using characteristic value information that indicates the relationship between the amount of light and the amount of change in the writing start timing; an update unit that calculates a change amount of the write start timing while the sensitivity is switched to each of the sensitivities by the sensitivity switching unit, and updates the characteristic values ​​that constitute the characteristic value information based on the change amount; An image forming apparatus having the same.

2. the sensitivity switching unit switches to one of a plurality of sensitivities, the control unit forms a first pattern for calculating a change amount of the write start timing; a detection unit that detects the density of the first pattern, the update unit calculates a change amount of the writing start timing based on the concentration detected by the detection unit; while switching between different sensitivities by the sensitivity switching unit, a process of forming the first pattern by the control unit, a process of detecting the density of the first pattern by the detection unit, and a process of calculating the amount of change in the writing start timing by the update unit are repeated; The update unit When one of the plurality of sensitivities is set as a reference sensitivity, the sensitivity corresponding to each of the calculation operations in the repetitive processing is divided by the reference sensitivity to calculate a ratio; 2. The image forming apparatus according to claim 1, wherein the amount of light from the light-emitting element when forming the first pattern is converted into an amount of light corresponding to the amount of change in each of the calculation operations by multiplying the amount of light by the respective ratios, and the characteristic values ​​constituting the characteristic value information are updated based on the amount of light and the amount of change.

3. The image forming apparatus of claim 2, wherein the correction unit calculates a correction value to eliminate the difference between the amount of change in the writing start timing that occurs when the light-emitting element is operated with the amount of light during printing operation and the amount of change in the writing start timing that occurs when the light-emitting element is operated with the amount of light during color matching to correct color misalignment between multiple colors.

4. 4. The image forming apparatus according to claim 3, wherein the light-emitting element when forming the first pattern and the detection unit that detects the density of the first pattern are the same as the light-emitting element when forming the second pattern used in the color matching and the detection unit that detects the density of the second pattern.

5. 5. The image forming apparatus according to claim 4, wherein the first pattern and the second pattern have the same angle, length, width and formation interval.

6. 5. The image forming apparatus according to claim 4, wherein the first pattern and the second pattern are formed with the same density.

7. 7. The image forming apparatus according to claim 2, wherein the control unit forms the first pattern using only the light emitting element that irradiates the light incident on the light detecting element.

8. 7. The image forming apparatus according to claim 2, wherein the sensitivity switching unit switches the sensitivity during the repeating process to include the sensitivity switching unit during a printing operation.

9. The image forming apparatus according to any one of claims 2 to 6, wherein the sensitivity switched by the sensitivity switching unit in the repeated processing includes a sensitivity equal to or greater than a value obtained by multiplying the ratio of the maximum light amount to the reference light amount, where the light amount of the light from the light-emitting element used during the printing operation is the reference light amount, by the sensitivity switched by the sensitivity switching unit during the printing operation.

10. The image forming apparatus according to any one of claims 2 to 6, wherein the sensitivity switched by the sensitivity switching unit in the repeated processing includes a sensitivity equal to or less than a value obtained by multiplying the ratio of a minimum light amount to a reference light amount, where the light amount of the light from the light-emitting element used during the printing operation is the reference light amount, by the sensitivity switched by the sensitivity switching unit during the printing operation.

11. further comprising a storage unit that stores the characteristic value information; 7. The image forming apparatus according to claim 1, wherein the characteristic value information stored in the memory unit is composed of characteristic values ​​corresponding to the sensitivity switched by the sensitivity switching unit during printing operation.

12. the updating unit updates the characteristic values ​​constituting the characteristic value information indicating a relationship between the amount of light and the amount of change for a specific sensitivity among the plurality of sensitivities; The image forming apparatus according to any one of claims 1 to 6, wherein the correction unit calculates the amount of change in the writing start timing at the sensitivity to be used using the characteristic value information corresponding to the specific sensitivity and the ratio between the sensitivity to be used and the specific sensitivity, and calculates a correction value corresponding to the amount of change.

13. the characteristic value information is information in a table format that associates the light amount with the amount of change in the writing start timing; An image forming apparatus according to any one of claims 2 to 6, wherein the update unit updates the characteristic values ​​constituting the characteristic value information by interpolation processing on a plot determined by the amount of change in the writing start timing calculated in the repetitive processing and the amount of light converted corresponding to the amount of change.

14. The image forming apparatus according to claim 13 , wherein the repeating process is performed while the sensitivity switching unit switches between three or four sensitivities.

15. 14. The image forming apparatus according to claim 13, wherein the interpolation processing is a linear interpolation processing.

16. the characteristic value information is a characteristic value curve expressed by an N-th degree polynomial that indicates the relationship between the amount of light and the amount of change in the writing start timing, The image forming apparatus according to any one of claims 2 to 6, wherein the update unit calculates coefficients of each order of an approximation equation for a plot determined by the amount of change in the writing start timing calculated in the repetitive processing and the amount of light converted corresponding to the amount of change, and updates the coefficients as the characteristic values ​​of the characteristic value curve.

17. The image forming apparatus according to claim 16, wherein the repeated process is performed while the sensitivity is switched to N+1 sensitivities by the sensitivity switching unit.

18. 17. The image forming apparatus according to claim 16, wherein the characteristic value curve is expressed by a third-order or fourth-order polynomial.

19. During a printing operation, an operation of calculating a correction value by the correction unit using the characteristic value information is enabled; 7. The image forming apparatus according to claim 3, wherein, during the color matching, an operation of the correction unit to calculate a correction value using the characteristic value information is disabled.

20. 7. The image forming apparatus according to claim 1, wherein the light emission control unit controls the amount of light emitted from the light emitting element to be constant throughout the entire period when the light scans the photosensitive member.

21. 7. The image forming apparatus according to claim 1, wherein the light detecting element detects light emitted from the plurality of light emitting elements.

22. 7. The image forming apparatus according to claim 1, wherein the light detecting element has a slit for restricting the direction of incidence of light.

23. 7. The image forming apparatus according to claim 1, wherein the plurality of sensitivities switched by the sensitivity switching unit are stored in a storage unit as values ​​actually measured in advance.

24. The image forming apparatus according to any one of claims 1 to 6, wherein the sensitivity switching circuit includes a resistor connected to the light detection element and a switching element that switches whether or not current is applied to the resistor in response to a signal from the sensitivity switching unit.

25. an optical writing device including the light emitting element, the deflector, and the light detecting element; The control unit detects whether the optical writing device has been replaced, An image forming apparatus as described in any one of claims 1 to 6, wherein when the control unit detects that the optical writing device has been replaced, the update unit calculates the amount of change in the writing start timing while the sensitivity switching unit switches to each of the sensitivities, and performs an operation of updating the characteristic values ​​that constitute the characteristic value information based on the amount of change.

26. 7. The image forming apparatus according to claim 1, wherein the control unit notifies the updater that the characteristic value of the characteristic value information has been updated when the updater updates the characteristic value.

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