Image forming device

Abstract

To provide an image forming device capable of reducing a decrease in productivity.SOLUTION: An image forming device comprises: a light-emitting element that irradiates light; a deflector that deflects light irradiated from the light-emitting element to scan a photoreceptor; a light detection element that detects light in order to determine a writing start timing for forming a latent image by scanning the photoreceptor with light irradiated from the light-emitting element via the deflector; a sensitivity switching circuit that switches a sensitivity of the light detection element for detecting light; a control unit having a light emission control section that controls a light amount of the light irradiated from the light-emitting element and a sensitivity switching section that switches the sensitivity via the sensitivity switching circuit according to a set light amount. The control unit determines whether to execute color shift correction on the basis of a deviation of the writing start timing when the sensitivity is switched by the sensitivity switching unit.SELECTED DRAWING: Figure 9

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 optical detection sensor determines whether or not laser light is input based on changes in the current. The intensity of the laser light changes depending on conditions, such as 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 intensity of the laser light from the laser diode also change the intensity of the laser light input to the optical detection sensor. In this case, if the fluctuation range of the laser light intensity incident on the optical detection sensor becomes large, a single gain cannot cover it. Furthermore, if the gain is too large, the optical detection sensor may detect light from an unexpected path (stray light) when the intensity of the laser light incident on the optical detection sensor is large. Conversely, if the gain is too small, the jitter in the detected waveform may worsen or the laser light may not be detected when the intensity of the laser light incident on the optical detection sensor is small. As a solution to this problem, a technology has been developed to switch the gain of the optical detection sensor according to the intensity of the laser light incident on the optical detection sensor.

[0003] Because the amount of laser light incident on the optical detection sensor is affected by environmental changes such as temperature and humidity, gain switching occurs during operation of the image forming apparatus. In other words, the basic control method is to switch to an appropriate gain depending on the amount of laser light to prevent erroneous detection of stray light and missed detection of laser light during operation of the image forming apparatus. Here, gain is a parameter that adjusts the sensitivity of laser light detection. A higher gain increases detection sensitivity, while a lower gain decreases detection sensitivity. If the detection sensitivity changes, the waveform of the laser light detected by the optical detection sensor changes, resulting in a shift in detection timing. This results in a shift in the start timing of image data writing, causing positional deviation in the scanning direction (main scanning direction), resulting in color variations and color shifts, and degrading image quality, which is particularly problematic in color machines.

[0004] To solve this problem, a control method is known in which color shift correction is performed after switching the gain. By performing color shift correction, the shift in the timing at which image data starts to be written due to the gain is also corrected, so if the color shift correction is completed properly, high-quality images can be provided.

[0005] As a technology for correcting such color shift, a control method has been disclosed in which color shift correction is performed after changing the detection sensitivity (gain switching) of the synchronization detection means in order to correct the shift in the writing start position that occurs when the detection sensitivity is changed (gain value switching) (for example, Patent Document 1). Summary of the Invention [Problem to be solved by the invention]

[0006] However, with conventional technology, when the gain is frequently switched, the above-mentioned color misregistration correction must be performed each time, and image formation operations must be stopped while the color misregistration correction is in progress. In addition, the supply costs for forming the color matching pattern increase, resulting in reduced productivity.

[0007] The present invention has been made in view of the above, and has an object to provide an image forming apparatus that can reduce a decrease in productivity. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the object, the present invention provides a control unit having: 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 onto the photosensitive element via the deflector; a sensitivity switching circuit that switches the sensitivity at which the light-detecting element detects the light; a light-emitting control unit that controls the amount of light irradiated by the light-emitting element; and a sensitivity switching unit that switches the sensitivity via the sensitivity switching circuit in accordance with the set light amount, wherein when the sensitivity is switched by the sensitivity switching unit, the control unit determines whether or not to perform color shift correction based on a shift in the write start timing. [Effects of the Invention]

[0009] According to the present invention, it is possible to reduce the decrease in productivity. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of an image forming apparatus according to the first 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 first embodiment. [Figure 3] FIG. 3 is a diagram illustrating a scanning operation of a laser beam in the image forming apparatus according to the first 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 first 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 first embodiment. [Figure 6] FIG. 6 is a diagram illustrating an example of the configuration of an optical writing device of the image forming apparatus according to the first embodiment. [Figure 7] FIG. 7 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 first embodiment, and the detection signal and output signal. [Figure 8] FIG. 8 is a diagram showing an example of the configuration of the synchronization detection plate of the image forming apparatus according to the first embodiment. [Figure 9] FIG. 9 is a diagram illustrating an example of the functional block configuration of the control device of the image forming apparatus according to the first embodiment. [Figure 10] FIG. 10 is a diagram illustrating a case where gain is switched to prevent erroneous detection of stray light for the synchronization detection plate of the image forming apparatus according to the first embodiment. [Figure 11] FIG. 11 is a diagram illustrating a case where gain is switched to prevent missed detection for the synchronization detection plate of the image forming apparatus according to the first embodiment. [Figure 12] FIG. 12 is a diagram illustrating a shift in the write start timing when the gain is switched in the image forming apparatus according to the first embodiment. [Figure 13] FIG. 13 is a diagram illustrating the operation when switching from a large gain to a small gain in the image forming apparatus according to the first embodiment. [Figure 14] FIG. 14 is a diagram illustrating the operation when the gain is switched from a small gain to a large gain in the image forming apparatus according to the first embodiment. [Figure 15] FIG. 15 is a diagram illustrating a gain switching operation when the image forming apparatus according to the first embodiment operates in a plurality of operation modes. [Figure 16] FIG. 16 is a flowchart showing an example of the flow of the printing operation of the image forming apparatus according to the first embodiment. [Figure 17]FIG. 17 is a flowchart showing an example of the flow of the density adjustment operation of the image forming apparatus according to the first embodiment. [Figure 18] FIG. 18 is a flowchart showing an example of the flow of the color matching operation of the image forming apparatus according to the first embodiment. [Figure 19] FIG. 19 is a diagram showing an example of the configuration of a synchronization detection plate of the image forming apparatus according to the second embodiment. [Figure 20] FIG. 20 is a diagram illustrating a shift in the write start timing when the gain is switched in the image forming apparatus according to the second embodiment. [Figure 21] FIG. 21 is a diagram illustrating the operation when the gain is switched from the medium gain to the small gain or the large gain in the image forming apparatus according to the second embodiment. [Figure 22] FIG. 22 is a diagram illustrating the operation when the large gain is switched to the medium gain or the small gain in the image forming apparatus according to the second embodiment. [Figure 23] FIG. 23 is a diagram illustrating a switching operation from a large gain to a medium gain or a small gain when the image forming apparatus according to the second embodiment operates in a plurality of operation modes. [Figure 24] FIG. 24 is a diagram illustrating a switching operation from a small gain to a medium gain or a large gain when the image forming apparatus according to the second embodiment operates in a plurality of operation modes. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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.

[0012] [First embodiment] (Configuration of image forming device) FIG. 1 is a diagram showing an example of the configuration of an image forming apparatus according to the first 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 the first embodiment. FIG. 3 is a diagram explaining the scanning operation of laser light in the image forming apparatus according to the first 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 the first 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 the first embodiment. The configuration of the image forming apparatus 1 according to this embodiment will be described with reference to FIGS. 1 to 5.

[0013] 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.

[0014] 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, image forming apparatus 1 includes transfer belt 40, transfer roller 42, density detector 45, 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] Note that photosensitive drums 30a, 30b, 30c, and 30d may be referred to simply as "photosensitive drum 30" when referring to any one of the photosensitive drums or collectively. 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 collectively. 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 collectively. Development 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 collectively. 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 collectively. 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."

[0020] 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. 9.

[0021] 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 FIG. 6.

[0022] 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).

[0023] 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.

[0024] 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.

[0025] The charging devices 32 are devices that uniformly charge the surfaces of the corresponding photosensitive drums 30 .

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] The home position sensor 46 is a sensor that detects the home position (original position) of the rotation of the corresponding photosensitive drum 30 .

[0032] 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.

[0033] 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 .

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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 FIG. 6. 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.

[0039] 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 narrow the direction of incident light in order to improve detection accuracy.

[0040] 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 it into a digital output signal (synchronization signal) that indicates the period during which the constant voltage is exceeded as 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.

[0041] 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.

[0042] (Configuration of optical writing device) 6 is a diagram showing an example of the configuration of an optical writing device of the image forming apparatus according to the first embodiment. The configuration of the optical writing device 20 of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG.

[0043] 6, the optical writing device 20 includes laser diodes 21a and 21b, 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. 9, which will be described later.

[0044] 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.

[0045] The lenses 22a and 22b are lenses that collimate the laser beams emitted from the laser diodes 21a and 21b, respectively, by using refraction.

[0046] The polygon mirror 23 is rotated by a polygon motor 23a (described later) and is a rotary polygonal mirror having a polygonal prism shape when viewed from 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 and incident on synchronization detection plates 90a and 90b before or after scanning the photosensitive drum 30.

[0047] 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. Since the width of the electrostatic latent image is the image width, the area outside the width of the electrostatic latent image formed on the photosensitive drum 30 is treated as outside the image area.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] As described above, the laser light emitted from each of the laser diodes 21a and 21b passes through the lenses 22a and 22b, the polygon mirror 23, and the fθ lenses 24a and 24b in this order, and reaches the photosensitive drum 30, where it forms an electrostatic latent image of each color image on the photosensitive drum 30.

[0052] 6 is merely an example, and other optical systems may be included. For example, the optical writing device 20 may have another set of each unit shown in FIG. 6 to form electrostatic latent images of the respective colors on the four photosensitive drums 30. In this case, the image forming apparatus 1 is provided with four synchronization detection plates 90, and the optical detection sensors 91 of each synchronization detection plate 90 detect the respective laser beams and output different synchronization signals for the respective colors to the control device 10.

[0053] (Configuration and operation of synchronous detection plate) Fig. 7 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 first embodiment and the detection signal and output signal. Fig. 8 is a diagram illustrating an example of the configuration of a synchronization detection plate 90 of the image forming apparatus according to the first embodiment. The configuration and operation of the synchronization detection plate 90 of the image forming apparatus 1 according to this embodiment will be described with reference to Figs. 7 and 8.

[0054] When the amount of laser light incident on the light detection sensor 91 fluctuates, the detection signal also changes. As shown in FIG. 7(a), 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 light 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 light detection sensor 91. Therefore, if the amount of laser light increases or decreases, the position of the edge changes, causing a shift in the write start timing.

[0055] 7(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.

[0056] 7(c) 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, causing the sensor to fail to detect the laser light and resulting in a malfunction.

[0057] 7(b) and 7(c), if the amount of laser light incident on the light detection sensor 91 becomes too large or too small, stray light can cause false detection or laser light detection failure. To solve this problem, the synchronization detection plate 90 of the image forming apparatus 1 according to this embodiment has a configuration for switching the gain of the light detection sensor 91, as shown in FIG.

[0058] 8, the synchronization detection plate 90 has a light detection sensor 91 and a gain switching circuit 92 (an example of a sensitivity switching circuit). The gain switching circuit 92 is a circuit for switching the gain that adjusts the detection sensitivity of the light detection sensor 91 in response to a gain switching signal input from the control device 10. The gain switching circuit 92 has a resistor R1, a resistor R2, and a switching element SW.

[0059] In such a synchronous detection plate 90, the value of the gain resistance of the light detection sensor 91 is switched by a gain switching signal (a signal input to the base of the switching element SW) input from the control device 10. In the example of the synchronous detection plate 90 shown in Fig. 8, when the gain switching signal input from the control device 10 is a low-level voltage, the value of the gain resistance becomes the value of resistor R1. On the other hand, when the gain switching signal input from the control device 10 is a high-level voltage, the gain resistance becomes the resistance when resistors R1 and R2 are connected in parallel, and its value is 1 / (1 / R1+1 / R2).

[0060] 8 is configured as an external circuit to the light detection sensor 91, the present invention is not limited to this and may be a circuit built into the light detection sensor 91. In the following, the gain switching circuit 92 will be described as an external circuit to the light detection sensor 91.

[0061] (Configuration and operation of the control device's functional blocks) Fig. 9 is a diagram showing an example of the configuration of functional blocks of a control device of an image forming apparatus according to the first embodiment. Fig. 10 is a diagram illustrating a case where gain is switched to prevent erroneous detection of stray light for the synchronous detection plate of the image forming apparatus according to the first embodiment. Fig. 11 is a diagram illustrating a case where gain is switched to prevent missed detection for the synchronous detection plate of the image forming apparatus according to the first embodiment. The configuration and operation of functional blocks of the control device 10 of the image forming apparatus 1 according to this embodiment will be described with reference to Figs. 9 to 11.

[0062] As shown in FIG. 9, 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, a gain switching unit 106 (sensitivity switching unit), a reference value memory unit 111, a correction value memory unit 112, and a gain switching memory unit 113.

[0063] 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.

[0064] 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 an on signal and an off signal corresponding to image data to the laser diode 21 in order to form an electrostatic latent image on the photosensitive drum 30 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. 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, this embodiment will be described assuming that the laser light is irradiated with a uniform amount of light throughout the entire laser light scanning period in order to reduce manufacturing costs.

[0065] 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.

[0066] The deflection control unit 104 is a functional unit that controls the rotation of the polygon motor 23a by controlling 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.

[0067] 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, by performing color misregistration correction through color matching operations, an electrostatic latent image can be formed at a targeted position on the photosensitive drum 30, making it possible to form a high-quality image.

[0068] The gain switching unit 106 is a functional unit that switches the gain 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] The above-mentioned sensor control unit 101, light emission control unit 102, counting unit 103, deflection control unit 104, correction value calculation unit 105, and gain switching unit 106 are realized by the 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, and gain switching unit 106 may be realized by a hardware circuit such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit).

[0073] Note that the functional units of the control device 10 shown in Fig. 9 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. 9, 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. 9 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. 9 may be divided into multiple functional units and configured as multiple functional units.

[0074] Here, as shown in FIG. 7(b) above, assume a situation in which the amount of laser light incident on the light detection sensor 91 is too large, resulting in erroneous detection of stray light. In this case, the gain switching signal output from the gain switching unit 106 is at a low level, the value of the gain resistor is the value of resistor R1 (hereinafter, in this embodiment, this may be referred to as a large gain) (first sensitivity), and the sensitivity of laser light detection is high (this may be referred to as a large gain) (waveform of the detection signal indicated by the dashed-dotted line in FIG. 10(b)). False detection of stray light occurs when the waveform of the detection signal exceeds the constant voltage (threshold) of the comparator. In this case, false detection of stray light can be prevented by reducing the voltage of the waveform of the detection signal, which is an analog value.

[0075] 10(a), the gain switching unit 106 switches the gain switching signal to a high level, thereby switching the value of the gain resistor to 1 / (1 / R1+1 / R2) (hereinafter, sometimes referred to as a small gain in this embodiment) (second sensitivity) which is smaller than the large gain (the value of resistor R1), thereby lowering the sensitivity of detecting the laser light (this may be referred to as a small gain). As a result, the waveform of the detection signal shown by the solid line in FIG. 10(b) becomes smaller than that in the case of a large gain, making it possible to prevent erroneous detection due to stray light.

[0076] Also, as shown in FIG. 7(c) above, assume a situation where the amount of laser light incident on the light detection sensor 91 is too small, resulting in a detection miss. In this case, the gain switching signal output from the gain switching unit 106 is at a high level, the value of the gain resistor is 1 / (1 / R1+1 / R2) (small gain), and the sensitivity of laser light detection is low (i.e., the gain is small) (the waveform of the detection signal indicated by the dashed-dotted line in FIG. 11(b)). A detection miss occurs when the waveform of the detection signal does not reach the constant voltage (threshold) of the comparator. In this case, a detection miss can be prevented by increasing the voltage of the waveform of the detection signal, which is an analog value.

[0077] Here, as shown in Fig. 11(a), the gain switching unit 106 switches the gain switching signal to low level, thereby switching the value of the gain resistor R1 to a value (large gain) larger than the small gain, and increasing the sensitivity of laser light detection (i.e., increasing the gain). As a result, the waveform of the detection signal shown by the solid line in Fig. 11(b) becomes larger than that in the case of a small gain, making it possible to prevent missed detections.

[0078] (Operation when switching the gain of the light detection sensor) Fig. 12 is a diagram illustrating a shift in write start timing when the gain is switched in the image forming apparatus according to the first embodiment. Fig. 13 is a diagram illustrating the operation when the gain is switched from a large gain to a small gain in the image forming apparatus according to the first embodiment. Fig. 14 is a diagram illustrating the operation when the gain is switched from a small gain to a large gain in the image forming apparatus according to the first embodiment. With reference to Figs. 12 to 14, the operation when the gain of the optical detection sensor 91 of the synchronization detection plate 90 is switched by the control device 10 of the image forming apparatus 1 according to this embodiment will be described.

[0079] As shown in FIG. 12(a), when the intensity of the laser light incident on the optical detection sensor 91 increases or decreases, the position of the falling edge or rising edge fluctuates, causing the write start timing to fluctuate. FIG. 12(b) is a graph showing the change in the write start timing when the optical detection sensor 91 has a large gain and when it has a small gain. As shown in FIG. 12(b), the relationship between the intensity of the laser light and the change in the write start timing is nonlinear; the smaller the intensity of the laser light, the greater the change in the write start timing. When the optical detection sensor 91 has a large gain, the allowable light intensity range of the laser light incident on the optical detection sensor 91 (the range of laser light intensity that can be used with a large gain) shifts downward. When the optical detection sensor 91 has a small gain, the allowable light intensity range of the laser light incident on the optical detection sensor 91 (the range of laser light intensity that can be used with a small gain) shifts upward. The double-headed arrows in FIG. 12(b) indicate the shift in the write start timing caused by the gain change. Even if color shift correction is performed before gain switching, a shift in the start timing of writing occurs when the gain is switched, resulting in degradation of image quality when the gain is switched. To solve this problem, a conventional method is known in which color shift correction is performed using the switched gain after the gain is switched. By controlling in this manner, the shift that occurs when the gain is switched can be suppressed by color shift correction, thereby providing high-quality images. However, if gain switching occurs frequently, color shift correction must be performed each time the gain is switched, which reduces productivity. Therefore, in this embodiment, a configuration that can reduce the frequency of gain switching will be described.

[0080] The relative positions of the two graphs shown in FIG. 12(b) are determined by the relationship between the values ​​of resistors R1 and R2 of the gain switching circuit 92 shown in FIG. 8. As the value of resistor R2 increases, the small-gain graph approaches the large-gain graph. As the value of resistor R2 decreases, the small-gain graph deviates from the large-gain graph. The shapes of the graphs also change depending on the values ​​of resistors R1 and R2. The usage of the image forming apparatus 1 determines the range of laser light intensity incident on the light detection sensor 91. Even if one gain cannot be used across the entire range of laser light intensity, a configuration that allows switching to another gain can ensure that the sensor can be used across the entire range of laser light intensity. The values ​​of resistors R1 and R2 must be determined so that the sensor can operate normally across the entire range of laser light intensity incident on the light detection sensor 91, preventing false detection and missed detection due to stray light.

[0081] Here, in the method of using the image forming apparatus 1, the minimum value of the range of the light intensity of the laser light incident on the light detection sensor 91 is defined as Pmin, and the maximum value is defined as Pmax. Furthermore, the minimum value of the range of the light intensity of the laser light that can be detected when the gain resistor is a large gain (the value of resistor R1) is defined as Pmin(R1), and the maximum value is defined as Pmax(R1). The minimum value that the value of resistor R1 can take is defined as R1min, and the maximum value that the value of resistor R2 can take is defined as R2min, and the maximum value is defined as R2max. In this case, the following equations (1) and (2) hold. Here, the MIN function in equation (1) is a function that returns the minimum value of its arguments.

[0082] Pmin(R1) / MIN(Pmax,Pmax(R1))×R1max ≦ 1 / (1 / R1max+1 / R2min) ···(1) 1 / (1 / R1min+1 / R2max) ≦ Pmax(R1) / Pmax×R1min (2)

[0083] Furthermore, by transforming equations (1) and (2), the following equations (3) and (4) are obtained.

[0084] Pmin(R1) / (MIN(Pmax,Pmax(R1))-Pmin(R1))×R1max ≦ R2min ···(3) R2max ≦ Pmax(R1) / (Pmax-Pmax(R1))×R1min (4)

[0085] In this case, by setting the value of resistor R2 within the range of R2min to R2max expressed by equations (3) and (4), it is possible to select resistor R2 that can be used in all ranges of laser light intensity in the usage of image forming apparatus 1.

[0086] It is also best to select the value of resistor R2 as close as possible to the maximum value, R2max. In other words, it is desirable to set it so that the two gains are close to each other. The closer the value of resistor R2 is to R2max, the smaller the shift in the large and small gain graphs becomes, minimizing the discrepancy in writing start timing that occurs when the gain is switched. Furthermore, the usable light intensity range is wider for both gains, reducing the frequency of gain switching and the frequency of color shift correction that operates in conjunction with gain switching.

[0087] Further transforming equation (4) yields the following equation (5): Here, since equation (4) is an equation for determining the value of resistor R2, the inequality is replaced with an equality. Also, since Pmax(R1) is the light intensity that is the threshold for large gain, the calculation formula on the right side indicates that it is involved in determining that threshold.

[0088] Pmax(R1)=(R2max / (R1min+R2max))×Pmax ···(5)

[0089] Here, the combined resistance value of resistors R1 and R2 is expressed as 1 / (1 / R1+1 / R2)=R1×R2 / (R1+R2). Further transforming the right-hand side of equation (5) yields the following equation (6). When the value of resistor R2 is selected to approach R2max, it approaches the relationship in equation (6). Therefore, Pmax(R1) approaches the relationship obtained by multiplying the combined resistance value by the maximum value Pmax of the light intensity range in image forming apparatus 1 and dividing it by the value of resistor R1.

[0090] Pmax(R1)=1 / (1 / R1min+1 / R2max) / R1min×Pmax...(6)

[0091] Here, the initial state is a state in which the light detection sensor 91 is operated at a large gain (the gain resistor has the value of resistor R1). At this time, as shown in FIG. 13A, if the amount of laser light incident on the light detection sensor 91 becomes too large, erroneous detection due to stray light occurs. To prevent erroneous detection due to stray light, the determination criterion is whether the amount of laser light exceeds Pmax (R1), which is the maximum usable amount of laser light. In a method of using the image forming apparatus 1, if the light amount setting for turning on the laser diode 21 exceeds Pmax (R1), which is the maximum usable amount of laser light incident on the light detection sensor 91, the gain switching unit 106 switches the gain of the light detection sensor 91 to a small gain, as shown in FIG. 13B. Since switching the gain causes a shift in the start timing of writing, the control device 10 operates to perform color misregistration correction before the start of the next printing operation.

[0092] Next, the initial state is a state in which the light detection sensor 91 is operated at a small gain (combined resistance of resistors R1 and R2, which are connected in parallel as a gain resistor). At this time, as shown in FIG. 14A, if the amount of laser light incident on the light detection sensor 91 becomes too small, a beam of light will not be detected. To prevent this, the criterion for determining whether the amount of laser light is below Pmin(R1, R2), the minimum usable amount of laser light. In the method of using the image forming apparatus 1, if the light amount setting for turning on the laser diode 21 is set to be below Pmin(R1, R2), the minimum usable amount of laser light incident on the light detection sensor 91, the gain switching unit 106 switches the gain of the light detection sensor 91 to a large gain, as shown in FIG. 14B. Since switching the gain causes a shift in the start timing of writing, the control device 10 operates to perform color registration correction before the next printing operation is started.

[0093] 13 and 14, the timing at which the gain switching unit 106 switches the gain is when the light intensity of the laser diode 21 exceeds the maximum value Pmax(R1) (first light intensity) when a large gain is used, and when the light intensity of the laser diode 21 falls below the minimum value Pmin(R1, R2) (second light intensity) when a small gain is used. That is, in the image forming apparatus 1 according to this embodiment, the light intensity conditions for switching the gain are different depending on the gain currently being used by the light detection sensor 91. That is, in the image forming apparatus 1, the light intensity for switching the gain is set separately for each gain.

[0094] The intensity of the laser beam emitted by the laser diode 21 varies depending on the density adjustment operation of the image forming apparatus 1. Even in the same environment, the intensity fluctuates due to variations in measurement results. If the gain switching threshold were set to a single point, the gain would be switched each time depending on the variations in the adjustment results, potentially resulting in color misregistration correction being performed each time, reducing productivity. To prevent this, appropriate resistance values ​​for resistors R1 and R2 are selected based on the above-described equations (3) and (4). The threshold light intensity for switching from a high gain to a low gain and the threshold light intensity for switching from a low gain to a high gain are separately set. As shown in Figures 13 and 14, the currently set gain is maintained as long as possible up to the upper and lower limits of the laser beam intensity range available for each gain. This minimizes the frequency of gain switching, reduces supply costs, and alleviates a decrease in productivity of the image forming apparatus 1.

[0095] Furthermore, in this embodiment, as will be described later with reference to FIG. 17, the control device 10 determines whether to perform color shift correction when switching the gain. Comparing the cases of FIG. 13 and FIG. 14, it can be seen that the gain switching in FIG. 13 does not result in as large a deviation in the write start timing as the gain switching in FIG. 14. This is because, in the waveform of the detection signal, which is the analog value of the light detection sensor 91, the deviation in detection timing is smaller when the waveform portion slightly exceeds the comparator value than when the waveform portion significantly exceeds the comparator value. In other words, when the gain switching unit 106 switches from a large gain to a small gain, the control device 10 may determine that the deviation in the write start timing is within the tolerance and may not perform color shift correction. On the other hand, when the gain switching unit 106 switches from a small gain to a large gain, the control device 10 may determine that the deviation in the write start timing is not within the tolerance and may perform color shift correction. In this way, by performing color misregistration correction only when it is determined that color misregistration correction is necessary when switching the gain, it is possible to reduce a decrease in productivity of the image forming apparatus 1.

[0096] (Gain switching operation when operating in multiple operating modes) 15 is a diagram illustrating a gain switching operation when the image forming apparatus according to the first embodiment operates in a plurality of operation modes. With reference to FIG. 15, a gain switching operation when the image forming apparatus 1 according to the present embodiment operates in a plurality of operation modes by the control device 10 will be described.

[0097] 12 to 14, the image forming apparatus 1 is assumed to use a specific laser beam intensity. In reality, the image forming apparatus 1 may operate with multiple laser beam intensities, rather than a single one, depending on factors such as productivity (linear speed) or output resolution. The laser beam intensity may also be switched by a user or service technician. When the intensity of the laser beam incident on the light detection sensor 91 changes, it may be necessary to switch the gain and perform color misregistration correction each time. Performing color misregistration correction each time the image forming apparatus 1 operates reduces productivity and increases supply costs. Therefore, in this embodiment, when the light-emission control unit 102 controls the laser diode 21 to light at different laser beam intensities in each of the image forming apparatus 1's multiple operating modes, the resistors R1 and R2 of the gain switching circuit 92 are selected so that at least one gain can be set to operate the light detection sensor 91 without switching the gain in all operating modes. When switching the gain of the light detection sensor 91, the gain switching unit 106 switches to a gain that does not require switching of the gain of the light detection sensor 91 in all operation modes. As a result, even if there are multiple types of laser light intensity used in each operation mode of the image forming apparatus 1, gain switching and color misregistration correction do not occur when the operation mode is switched, and a decrease in productivity of the image forming apparatus 1 can be reduced.

[0098] The shaded light intensity ranges shown in Figures 15(a) and 15(b) indicate the light intensity range of the laser light used in each operation mode, which can be switched depending on the current temperature and humidity environment, etc. The gain switching unit 106 switches the gain so that gain switching is not required for any light intensity within the light intensity range. Referring to Figure 15, a method for determining the gain so that the light detection sensor 91 can operate in all operation modes without gain switching will be described.

[0099] First, the minimum allowable light amount Pmin(R1, R2) of the laser light incident on the light detection sensor 91 is expressed by the following equation (7).

[0100] Pmin(R1,R2)=Pmin(R1)×R1max / (1 / (1 / R1max+1 / R2min)) =Pmin(R1)×(1+R1max / R2min) ···(7)

[0101] Then, by dividing the above-mentioned equation (5) by the equation (7), the following equation (8) is obtained.

[0102] Pmax(R1) / Pmin(R1,R2) =(1 / (1 / R1min+1 / R2max) / R1min) ×(1 / (1 / R1max+1 / R2min) / R1max) ×(Pmax / Pmin(R1)) (8)

[0103] This equation (8) shows the ratio between Pmax(R1), which is the threshold light amount when switching from a large gain to a small gain, and Pmin(R1, R2), which is the threshold light amount when switching from a small gain to a large gain. Furthermore, if we assume that the resistance values ​​of resistors R1 and R2 have small variations and are all replaced with typical values, the following equation (9) can be expressed.

[0104] Pmax(R1) / Pmin(R1,R2) =(1 / (1 / R1+1 / R2) / R1) 2 ×(Pmax / Pmin(R1)) ···(9)

[0105] As described above, the amount of laser light emitted from laser diode 21 during printing varies depending on factors such as productivity (linear speed) and output resolution. If the ratio of the maximum amount of light to the minimum amount of light used in a plurality of operation modes of image forming apparatus 1 is β, then selecting resistors R1 and R2 having resistance values ​​such that the calculation result of equation (9) is greater than β will enable at least one gain to be switched so that light detection sensor 91 can operate in all operation modes without switching the gain. Once gain switching unit 106 switches to such a gain, it can continue operation without switching to another gain thereafter, eliminating the need for color misregistration correction and reducing a decrease in productivity of image forming apparatus 1.

[0106] (Flow of printing operation of image forming device) 16 is a flowchart showing an example of the flow of the printing operation of the image forming apparatus 1 according to the first 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.

[0107] <Step S11> The control device 10 of the image forming apparatus 1 executes pre-processing for the printing operation. During the pre-processing by the control device 10, the gain switching unit 106 switches the gain of the light detection sensor 91 by the method shown in Figs. 13 to 15 depending on the amount of laser light from the laser diode 21 used in the operation of the image forming apparatus 1. Then, the process proceeds to step S12.

[0108] <Step S12> The light emission control unit 102 of the control device 10 reads out the gain information stored in the gain switching storage unit 113, and initializes the laser diode 21 with the read gain, and then proceeds to step S13.

[0109] <Step S13> If the initialization of the laser diode 21 has been performed normally (step S13: Yes), the process proceeds to step S14, and if the initialization has not been performed normally (step S13: No), the process proceeds to step S20.

[0110] <Step S14> 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 S14: Yes), the process proceeds to step S15, and if not (step S14: No), the process proceeds to step S20.

[0111] <Step S15> The control device 10 reads out the color matching execution conditions. Specifically, the control device 10 reads out the gain information stored in the color matching operation shown in Fig. 18, which will be described later. Then, the process proceeds to step S16.

[0112] <Step S16> The light emission control unit 102 adjusts the timing at which writing starts with the laser light from the laser diode 21. Then, the process proceeds to step S17.

[0113] <Step S17> The control device 10 executes the printing process, and then proceeds to step S18.

[0114] <Step S18> If all print jobs have been completed (step S18: Yes), the process proceeds to step S19, and if not (step S18: No), the process returns to step S15.

[0115] <Step S19> The control device 10 executes post-printing processing and then ends the printing operation.

[0116] <Step S20> The control device 10 executes a forced print termination process to terminate the printing operation, and then terminates the printing operation.

[0117] (Flow of density adjustment operation of image forming device) 17 is a flowchart showing an example of the flow of the density adjustment operation of the image forming apparatus 1 according to the first embodiment. The flow of the density adjustment operation of the image forming apparatus 1 according to this embodiment will be described with reference to FIG. 17. When a request to perform density adjustment occurs while the image forming apparatus 1 is in operation, the following density adjustment operation is performed at a predetermined timing.

[0118] <Step S31> The control device 10 of the image forming apparatus 1 executes pre-detection processing, and then the process proceeds to step S32.

[0119] <Step S32> The control device 10 forms a density adjustment pattern, which is a pattern for density adjustment, and then proceeds to step S33.

[0120] <Step S33> The control device 10 causes the density detector 45 to detect the toner density of the formed density adjustment pattern, and then the process proceeds to step S34.

[0121] <Step S34> The control device 10 calculates the amount of laser light emitted by the laser diode 21. Then, the process proceeds to step S35.

[0122] <Step S35> The control device 10 determines whether the calculated light amount is a normal value. If the light amount is a normal value (step S35: Yes), the process proceeds to step S36, and if the light amount is not a normal value (step S35: No), the density adjustment operation ends.

[0123] <Step S36> The control device 10 stores or updates the calculated light amount of the laser diode 21 in the storage device, and then proceeds to step S37.

[0124] <Step S37> The gain switching unit 106 of the control device 10 determines whether gain switching is necessary. Specifically, when the light detection sensor 91 is operating at a large gain, the gain switching unit 106 determines whether the amount of laser light incident on the light detection sensor 91 exceeds the above-mentioned Pmax (R1). Furthermore, when the light detection sensor 91 is operating at a small gain, the gain switching unit 106 determines whether the amount of laser light incident on the light detection sensor 91 is below the above-mentioned Pmin (R1, R2). If the amount of light exceeds the above-mentioned Pmax (R1) or if the amount of laser light incident on the light detection sensor 91 is below the above-mentioned Pmin (R1, R2) (step S37: Yes), it is determined that gain switching is necessary, and the process proceeds to step S38. If not (step S37: No), the density adjustment operation is terminated.

[0125] <Step S38> The gain switching unit 106 switches the gain of the light detection sensor 91. Specifically, when the light detection sensor 91 is operating at a large gain, the gain switching unit 106 switches the gain of the light detection sensor 91 to a small gain. On the other hand, when the light detection sensor 91 is operating at a small gain, the gain switching unit 106 switches the gain of the light detection sensor 91 to a large gain. Then, the gain switching unit 106 stores or updates information about the switched gain in the gain switching memory unit 113. Then, the process proceeds to step S39.

[0126] <Step S39> The control device 10 determines whether color misregistration correction is necessary. For example, when the gain switching unit 106 switches from a large gain to a small gain, the control device 10 determines that the deviation in the write start timing is within the allowable range and determines that color misregistration correction is not necessary. On the other hand, when the gain switching unit 106 switches from a small gain to a large gain, the control device 10 determines that the deviation in the write start timing is not within the allowable range and determines that color misregistration correction is necessary. By performing such a determination operation, it is possible to reduce the frequency of color misregistration correction and to alleviate a decrease in productivity of the image forming apparatus 1. If color misregistration correction is necessary (step S39: Yes), the process proceeds to step S40. If color misregistration correction is not necessary (step S39: No), the density adjustment operation ends.

[0127] <Step S40> Then, the control device 10 issues a request to perform color misregistration correction, and then ends the density adjustment operation.

[0128] (Flow of color matching operation of image forming device) Fig. 18 is a flowchart showing an example of the flow of the color matching operation of the image forming apparatus according to the first 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. 18. When a request to perform color misregistration correction occurs while the image forming apparatus 1 is in operation, the following color matching operation is performed at a predetermined timing.

[0129] <Step S51> The control device 10 of the image forming apparatus 1 executes pre-detection processing, and then the process proceeds to step S52.

[0130] <Step S52> The control device 10 forms a color matching pattern, which is a pattern for color matching, and then proceeds to step S53.

[0131] <Step S53> The control device 10 causes the density detector 45 to detect the toner density of the formed color matching pattern, and then the process proceeds to step S54.

[0132] <Step S54> The control device 10 determines whether or not the detection of the color matching pattern was successful. If the detection was successful (step S54: Yes), the process proceeds to step S55, and if the detection was not successful (step S54: No), the color matching operation ends.

[0133] <Step S55> The correction value calculation unit 105 of the control device 10 calculates the correction value using the detection result of the color matching pattern, and then the process proceeds to step S56.

[0134] <Step S56> 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 S56: Yes), the process proceeds to step S57, and if the correction value is not a normal value (step S56: No), the color matching operation ends.

[0135] <Step S57> 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 S58.

[0136] <Step S58> Then, the gain switching unit 106 stores the gain information (gain switching signal settings, resistance values, etc.) used when the color matching operation was performed in the gain switching storage unit 113. Then, the color matching operation is completed.

[0137] As described above, in the image forming apparatus 1 according to this embodiment, the laser diode 21 emits light, the polygon mirror 23 deflects the laser light emitted from the laser diode 21 to scan the photosensitive drum 30, the light detection sensor 91 detects the laser light to determine the write start timing for forming a latent image by scanning the laser light emitted from the laser diode 21 onto the photosensitive drum 30 via the polygon mirror 23, the gain switching circuit 92 switches the gain for the light detection sensor 91 to detect the laser light, and the control device 10 includes an emission control unit 102 that controls the amount of laser light emitted by the laser diode 21 and a gain switching unit 106 that switches the gain via the gain switching circuit 92 in accordance with the set light amount. When the gain switching unit 106 switches the gain, the control device 10 determines whether to perform color misregistration correction based on a deviation in the write start timing. This reduces the frequency of color misregistration correction, which is performed in accordance with gain switching, and reduces a decrease in productivity of the image forming apparatus 1.

[0138] [Second embodiment] The image forming apparatus 1 according to the second embodiment will be described, focusing on the differences from the image forming apparatus 1 according to the first embodiment. In the first embodiment, the operation of switching between two types of gain for the optical detection sensor 91 was described. In this embodiment, the operation of switching between three or more types of gain for the optical detection sensor 91 will be described. Note that the configuration of the image forming apparatus 1, the configuration of the optical writing device 20, and the configuration of the functional blocks of the control device 10 according to this embodiment are the same as the configurations described in the first embodiment.

[0139] (Configuration and operation of synchronous detection plate) Fig. 19 is a diagram showing an example of the configuration of a synchronization detection plate 90a of an image forming apparatus 1 according to the second embodiment. The configuration and operation of the synchronization detection plate 90a of the image forming apparatus 1 according to the present embodiment will be described with reference to Fig. 19.

[0140] In this embodiment, a configuration will be described in which there are two or more types of gain switching signals input from the control device 10. The number of gain switching signals input from the outside increases by the number of resistors (R1, R2, ...) provided on the gain switching circuit. The gain of the gain switching circuit is then switched by switching the voltage of each gain switching signal to either a high level or a low level. In this case, the number of gains that can be switched is a maximum of 2 n 1 (n: number of gain switching signals). For example, in the gain switching circuit 92 shown in FIG. 8, if there is one gain switching signal (n=1), the gain can be switched to a maximum of two different gains. When the number of gain switching signals is n, the gain can be switched to a maximum of 2n different gains. However, since it is difficult to set all 2n different gains to appropriate constants, by selecting and using only n+1 different gains from the 2n different gains, it becomes possible to operate the image forming apparatus 1 at a gain that is suitable for its intended use. In this embodiment, a configuration in which there are two gain switching signals (n=2) will be described, and a case in which n+1 different gains, i.e., three different gains, will be described. In this way, by using only gains selected in advance from a maximum of four different gains, it becomes possible to operate the image forming apparatus 1 at a gain that is suitable for its intended use.

[0141] 19, the synchronization detection plate 90a includes a light detection sensor 91 and a gain switching circuit 92a (an example of a sensitivity switching circuit). The gain switching circuit 92a is a circuit for switching the gain that adjusts the detection sensitivity of the light detection sensor 91 using two types of gain switching signals input from the control device 10. The gain switching circuit 92a includes resistors R1, R2, R3, switching elements SW1, and SW2.

[0142] In such a synchronization detection board 90a, the value of the gain resistor that serves as the basis for switching the gain of the photodetection sensor 91 is switched by two types of gain switching signals (signals input to the bases of the switching elements SW1 and SW2 respectively) input from the control device 10. In the example of the synchronization detection board 90a shown in FIG. 19, when both of the two types of gain switching signals input from the control device 10 are voltages of the Low level, the value of the gain resistor becomes the value of the resistor R1 (hereinafter, may be referred to as high gain in this embodiment) (third sensitivity). Further, when the gain switching signal input to the base of the switching element SW1 from the control device 10 is a voltage of the High level and the gain switching signal input to the base of the switching element SW2 is a voltage of the Low level, the gain resistor becomes the resistor when the resistors R1 and R2 are connected in parallel, and its value is 1 / (1 / R1 + 1 / R2) < R1) (hereinafter, may be referred to as medium gain in this embodiment) (fourth sensitivity). Further, when both of the two types of gain switching signals input from the control device 10 are voltages of the High level, the gain resistor becomes the resistor when the resistors R1, R2, and R3 are connected in parallel, and its value is 1 / (1 / R1 + 1 / R2 + 1 / R3) < 1 / (1 / R1 + 1 / R2) (hereinafter, may be referred to as low gain in this embodiment) (fifth sensitivity).

[0143] Note that the gain switching circuit 92a shown in FIG. 19 is configured as an external circuit with respect to the photodetection sensor 91, but is not limited thereto, and may be a circuit built in the photodetection sensor 91. Hereinafter, the gain switching circuit 92a will be described as an external circuit with respect to the photodetection sensor 91.

[0144] <000​​​​​ As described above, the gain switching circuit 92a can switch between three gains. Here, in a method of using the image forming apparatus 1, when the minimum value of the range of the amount of laser light incident on the light detection sensor 91 is Pmin and the maximum value is Pmax, a combination of the resistance values ​​of the resistors R1 to R3 to be used is determined. A relational expression is established between each pair of adjacent gains (a combination of a large gain and a medium gain, and a combination of a medium gain and a small gain). Furthermore, when the gain resistor is a large gain (the value of resistor R1), the minimum value of the range of the amount of laser light detectable is Pmin(R1), and the maximum value is Pmax(R1). The minimum value that resistor R1 can take is R1min, and the maximum value is R1max. The minimum value that resistor R2 can take is R2min, and the maximum value is R2max. The minimum value that resistor R3 can take is R3min, and the maximum value is R3max. In this case, the following equations (10) and (11) hold. Here, the MIN function in equation (10) is a function that returns the minimum value among the arguments.

[0146] Pmin(R1) / MIN(Pmax / α n-1-i(i=1) ,Pmax(R1))×R1max ≦ 1 / (1 / R1max+1 / R2min) ···(10) 1 / (1 / R1min+1 / R2max) ≦ Pmax(R1) / (Pmax / α n-1-i(i=1) )×R1min (11)

[0147] The coefficient α in the above equations (10) and (11) is a numerical value expressed by the following equation (12): In this embodiment, in order to maximize the range that each gain (large, medium, small) can cover, the coefficient α is set so that the ratio of the medium gain to the large gain and the ratio of the small gain to the medium gain are the same.

[0148] α = n-1 √(Pmax / Pmax(R1)) (12)

[0149] Furthermore, by transforming equations (10) and (11), the following equations (13) and (14) are obtained (n=2).

[0150] Pmin(R1) / (MIN(Pmax / α,Pmax(R1))-Pmin(R1))×R1max ≦ R2min ···(13) R2max ≦ (α×Pmax(R1)) / (Pmax-α×Pmax(R1))×R1min ···(14)

[0151] Similarly, a relational expression is established for the combination of medium gain and small gain. If the minimum value of the range of detectable laser light intensity when the gain resistor is medium gain (the combined resistance value of resistors R1 and R2) is Pmin(R1, R2) and the maximum value is Pmax(R1, R2), the following expressions (15) and (16) are established.

[0152] Pmin(R1,R2) / MIN(Pmax / α n-1-i(i=2) ,Pmax(R1,R2))×1 / (1 / R1max+1 / R2min) ≦ 1 / (1 / R1max+1 / R2min+1 / R3min) ···(15) 1 / (1 / R1min+1 / R2max+1 / R3max)≦Pmax(R1,R2) / (Pmax / α n-1-i(i=2) )×1 / (1 / R1min+1 / R2max) ···(16)

[0153] Furthermore, by transforming equations (15) and (16), the following equations (17) and (18) are obtained.

[0154] Pmin(R1,R2) / ((MIN(Pmax,Pmax(R1,R2))-Pmin(R1,R2))×(1 / R1max+1 / R2min)) ≦ R3min ···(17) R3max ≦ (Pmax(R1,R2)) / ((Pmax-Pmax(R1,R2))×(1 / R1min+1 / R2max))...(18)

[0155] In this case, it is best to select values ​​for resistors R2 and R3 as close as possible to their respective maximum values, R2max and R3max. The closer the values ​​of resistors R2 and R3 are to R2max and R3max, the smaller the shift in the gain graphs becomes, widening the usable range for any gain. This reduces the frequency of gain switching and the frequency of color shift correction, which operates in conjunction with gain switching.

[0156] Note that even if the number of gain switching signals increases, the calculation method is the same as above. That is, by calculating the value of resistor R1 in order, followed by the values ​​of resistors R2, R3, etc., it is possible to calculate the combination of resistor values ​​R1, R2, R3, etc. that maximizes the range that each can cover.

[0157] As mentioned above, it is recommended to select resistors R2 and R3 as close as possible to their respective maximum values, R2max and R3max. Ideally, R2max and R3max are the ideal values. However, the resistors R2 and R3 available on the market are limited, and their constants are somewhat fixed. Therefore, it is difficult to simply adopt the R2max and R3max constants calculated using the above calculation. Furthermore, because resistance components themselves vary, resistors R2 and R3 must be selected taking this variation into account. Therefore, it is practical to select resistors R2 and R3 with resistance values ​​as close as possible to R2max and R3max. However, even if the ideal resistance values ​​R2max and R3max cannot be adopted, the above-mentioned effects can be achieved by using resistors R2 and R3 with resistance values ​​close to R2max and R3max. Furthermore, if the ratio of medium gain to large gain and the ratio of small gain to medium gain are approximately the same, the above-mentioned effects can be determined to be achieved.

[0158] Furthermore, in this embodiment, calculations were performed for three cases: when both types of gain switching signals are Low-level voltage; when the gain switching signal input to the base of switching element SW1 is High-level voltage and the gain switching signal input to the base of switching element SW2 is Low-level voltage; and when both types of gain switching signals are High-level voltage. However, a configuration may also be used in which the gain switching signal input to the base of switching element SW1 is Low-level voltage and the gain switching signal input to the base of switching element SW2 is High-level voltage. In other words, as long as the combined resistance value used is the target resistance value, the above-mentioned effects can be achieved even if different combinations of gain switching signals are used.

[0159] (Operation when switching the gain of the light detection sensor) Fig. 21 is a diagram illustrating the operation when switching from a medium gain to a small gain or a large gain in the image forming apparatus according to the second embodiment. Fig. 22 is a diagram illustrating the operation when switching from a large gain to a medium gain or a small gain in the image forming apparatus according to the second embodiment. With reference to Figs. 21 and 22, the operation when switching the gain of the optical detection sensor 91 of the synchronization detection plate 90a by the control device 10 of the image forming apparatus 1 according to this embodiment will be described.

[0160] First, the initial state is a state in which the light detection sensor 91 is operated at a medium gain (the gain resistance is the combined resistance value of resistors R1 and R2). Then, in a method of using the image forming apparatus 1, if the light intensity setting when turning on the laser diode 21 exceeds Pmax(R1, R2), which is the maximum usable light intensity of the laser light incident on the light detection sensor 91, the gain switching unit 106 switches the gain of the light detection sensor 91 to a small gain, as shown in FIG. 21. Also, in a method of using the image forming apparatus 1, if the light intensity setting when turning on the laser diode 21 is below Pmin(R1, R2), which is the maximum usable light intensity of the laser light incident on the light detection sensor 91, the gain switching unit 106 switches the gain of the light detection sensor 91 to a large gain, as shown in FIG.

[0161] In this way, when a medium gain (medium gain in this case) is being used among the multiple gains, the upper and lower limit light amounts that are the thresholds for switching to another gain are set separately. Then, as shown in Fig. 21 above, by continuing to use the currently set gain as much as possible up to the upper and lower limits of the range of laser light amount that can be used for each gain, it is possible to minimize the frequency of gain switching, reduce increases in supply costs, and mitigate decreases in productivity of the image forming apparatus 1.

[0162] Furthermore, in this embodiment, the control device 10 determines whether to perform color shift correction when the gain is switched. That is, when the gain switching unit 106 switches from a large gain to a small gain, the control device 10 may determine that the deviation in the write start timing is within the allowable range and may not perform color shift correction. On the other hand, when the gain switching unit 106 switches from a small gain to a large gain, the control device 10 may determine that the deviation in the write start timing is not within the allowable range and may perform color shift correction. In this way, by performing color shift correction only when it is determined that color shift correction is necessary when the gain is switched, it is possible to reduce a decrease in productivity of the image forming apparatus 1.

[0163] Next, a state in which the light detection sensor 91 is operated at a large gain (the gain resistor is the resistance value of resistor R1) is set as an initial state. Then, in a method of using the image forming apparatus 1, if the light intensity setting for turning on the laser diode 21 exceeds Pmax(R1), which is the maximum usable light intensity of the laser light incident on the light detection sensor 91, the gain switching unit 106 switches the gain of the light detection sensor 91 to a medium gain or a small gain, as shown in FIG. 22. In this case, unlike FIG. 21, the gain switching unit 106 needs to perform a process of selecting an optimal gain to which to switch.

[0164] First, if the light intensity of the laser light incident on the light detection sensor 91 after the light intensity setting of the laser diode 21 is changed falls within the range of "small gain only" shown in Fig. 22, the gain switching unit 106 switches from large gain to small gain because normal operation is possible only with small gain.

[0165] Next, if the light intensity of the laser beam incident on the light detection sensor 91 after the light intensity setting of the laser diode 21 is changed falls within the range of "medium and small gains only" shown in FIG. 22, the gain switching unit 106 must select the optimal gain from the medium gain and the small gain. To do this, the gain switching unit 106 determines which range the currently set light intensity of the laser beam falls within. For example, if the currently set light intensity of the laser beam falls within the range of "large and medium gains only" shown in FIG. 22 and the gain is switched to medium, both the currently set light intensity and the light intensity after the setting change fall within the usable range of laser beam intensity. In this case, the gain switching unit 106 switches from large gain to medium gain. This is because there is a possibility that the light intensity will return to the currently set light intensity. The light intensity of the laser beam changes due to environmental changes such as temperature and humidity. If a long time has passed since the last density adjustment operation was performed and the environment has changed significantly, it is expected that the light intensity after the setting change will differ significantly, as described above. It is also expected that the currently set light intensity will return to a more preferable environment. If the current light intensity and the light intensity after the setting change can both be operated at the same gain (medium gain in this case), there is no need to switch the gain even if there is an environmental change in temperature, humidity, or the like in the usage environment of the image forming apparatus 1. In other words, there is no need to perform color misregistration correction, which must be performed every time the gain is switched, and a decrease in productivity of the image forming apparatus 1 can be reduced.

[0166] However, if the light intensity of the laser beam incident on the light detection sensor 91 after the light intensity setting of the laser diode 21 is changed falls within the range of "medium and small gains only" shown in FIG. 22, and if the currently set light intensity of the laser beam falls within the range of "any gain usable range" or "large gain only" shown in FIG. 22, it is impossible to determine whether to switch to a medium or small gain. Therefore, the gain switching unit 106 performs another determination process. Specifically, the gain switching unit 106 determines which of the ranges of light intensity usable after the gain change the light intensity will be closest to the center, and switches to the gain of the light intensity range that brings the light intensity closest to the center. Here, for a medium gain, the usable light intensity range is from Pmin(R1, R2) to Pmax(R1, R2), and for a small gain, the usable light intensity range is from Pmin(R1, R2, R3) to Pmax(R1, R2, R3). When the light intensity of the laser light after the setting change is P(Now), the gain switching unit 106 switches to the smaller gain of the following equations (19) and (20). The ABS function in equations (19) and (20) is a function that returns the absolute value of its argument.

[0167] ABS((Pmax(R1,R2)+Pmin(R1,R2)) / 2-P(Now)) ···(19) ABS((Pmax(R1,R2,R3)+Pmin(R1,R2,R3)) / 2-P(Now)) ···(20)

[0168] By using at least one of the above-described determinations, it is possible to minimize the frequency of gain switching, and therefore the frequency of performing color misregistration correction, and reduce any decline in productivity of the image forming apparatus 1. These determination processes are executed in step S38 shown in FIG. 17 above.

[0169] In the above-described FIG. 21 , when the gain switching unit 106 switches from a large gain to a small gain, the control device 10 determines that the deviation in the write start timing is within the tolerance and may not perform color shift correction. However, in reality, as shown in FIG. 22 , a certain deviation in the write start timing occurs when the gain is switched. The deviation increases as the difference in gain resistance before and after the switch increases. Therefore, the control device 10 may determine whether the deviation in the write start timing occurring when the gain is switched is within the tolerance, and may not perform color shift correction if it is within the tolerance, and may perform color shift correction if it is outside the tolerance. For example, in FIG. 22 , the deviation in the write start timing occurring when switching from a large gain to a medium gain may be considered within the tolerance, while the deviation in the write start timing occurring when switching from a large gain to a small gain may be considered outside the tolerance. Furthermore, to estimate the deviation in the write start timing due to the gain switch, gain information before the switch (such as the gain switching signal setting or resistance value) may be stored in the gain switching memory unit 113. This gain information is updated when the color shift correction is successfully completed. This minimizes the frequency of performing color misregistration correction, and reduces the decrease in productivity of the image forming apparatus 1.

[0170] (Gain switching operation when operating in multiple operating modes) Fig. 23 is a diagram illustrating a switching operation from a large gain to a medium gain or a small gain when the image forming apparatus according to the second embodiment operates in multiple operation modes. Fig. 24 is a diagram illustrating a switching operation from a small gain to a medium gain or a large gain when the image forming apparatus according to the second embodiment operates in multiple operation modes. With reference to Figs. 23 and 24, the gain switching operation when the image forming apparatus 1 according to the present embodiment operates in multiple operation modes will be described.

[0171] 15 described above, when the light emission control unit 102 controls the laser diode 21 to light up with different laser light intensity settings in each of the multiple operation modes of the image forming apparatus 1, the resistors R1 to R3 of the gain switching circuit 92 are selected so that at least one gain can be set that allows operation without switching the gain of the light detection sensor 91 in all operation modes. When switching the gain of the light detection sensor 91, the gain switching unit 106 switches the gain of the light detection sensor 91 to a gain that does not require switching the gain of the light detection sensor 91 in all operation modes. As a result, even if there are multiple types of laser light intensity used in each operation mode of the image forming apparatus 1, gain switching and color misregistration correction do not occur when switching the operation mode, and a decrease in productivity of the image forming apparatus 1 can be reduced.

[0172] 23(a) and 23(b) show the range of laser light intensity used in each operation mode that can be switched depending on the current temperature and humidity environment, and the current gain of the light detection sensor 91 is assumed to be large. The amount of laser light used changes due to density adjustment operations of the image forming apparatus 1, and the amount of laser light incident on the light detection sensor 91 changes accordingly.

[0173] For example, assume that the laser light intensity range has changed to "laser light intensity range used in multiple operation modes" in Fig. 23(a). In this case, the "laser light intensity range used in multiple operation modes" is included in the laser light intensity range in which a small gain can be used, and the gain switching unit 106 switches from the large gain to the small gain so that the gain used in the multiple operation modes of the image forming apparatus 1 is not switched.

[0174] Also, assume that the laser beam intensity range has changed to the "laser beam intensity range used in multiple operation modes" in FIG. 23(b). In this case, the "laser beam intensity range used in multiple operation modes" is included in both the laser beam intensity range in which a medium gain can be used and the laser beam intensity range in which a small gain can be used. Therefore, in order to prevent the gain used by the multiple operation modes of the image forming apparatus 1 from being switched, the gain switching unit 106 can switch from the large gain to the medium gain or the small gain. In this case, the gain switching unit 106 switches to the optimal gain using the same determination process as in FIG. 22. That is, the gain switching unit 106 determines which range the currently set laser beam intensity range falls within. In the example shown in FIG. 23(b), the currently set laser beam intensity range (currently used light intensity range) is included in the laser beam intensity range in which a medium gain can be used, but is not included in the laser beam intensity range in which a small gain can be used. In this case, the gain switching unit 106 switches from the large gain to the medium gain.

[0175] If the gain switching unit 106 makes the above determination and is unable to determine whether the gain should be switched to the medium gain or the small gain, the gain switching unit 106 performs another determination process, as in FIG. 22 . Specifically, the gain switching unit 106 determines which of the available light intensity ranges after the setting change will be closest to the center, and switches to the gain of the available light intensity range that will bring the light intensity range closest to the center. Here, in the case of a medium gain, the available light intensity range is the range from Pmin(R1,R2) to Pmax(R1,R2), and in the case of a small gain, the available light intensity range is the range from Pmin(R1,R2,R3) to Pmax(R1,R2,R3). When the light intensity range of the laser light after the setting change is set to Pmin(Now) to Pmax(Now), the gain switching unit 106 switches to the smaller gain of the following equations (21) and (22). The ABS function in equations (21) and (22) is a function that returns the absolute value of an argument.

[0176] ABS((Pmax(R1,R2)+Pmin(R1,R2)) / 2-(Pmax(Now)+Pmin(now)) / 2) ···(21) ABS((Pmax(R1,R2,R3)+Pmin(R1,R2,R3)) / 2-(Pmax(Now)+Pmin(now)) / 2)...(22)

[0177] By using at least one of the above-described determinations, it is possible to minimize the frequency of gain switching, and therefore the frequency of performing color misregistration correction, and reduce the decrease in productivity of the image forming apparatus 1. These determination processes are executed in step S38 shown in FIG. 17 above.

[0178] As in the cases shown in Figures 21 and 22 above, the control device 10 may not perform color shift correction processing if the shift in writing start timing that occurs when switching gain is within an acceptable range, but may perform color shift correction if it is outside the acceptable range.

[0179] The "light intensity range of laser light used in multiple operation modes" shown in Figures 24(a) and 24(b) indicates the light intensity range of laser light used in each operation mode that can be switched depending on the current temperature and humidity environment, and the current gain of light detection sensor 91 is assumed to be small. The light intensity of laser light used changes due to density adjustment operations, etc. of image forming apparatus 1, and the light intensity of laser light incident on light detection sensor 91 changes accordingly. In this case, too, gain switching unit 106 switches to the optimal gain based on the same determination criteria as those described above in Figure 23.

[0180] For example, assume that the laser light intensity range has changed to "laser light intensity range used in multiple operation modes" in Fig. 24(a). In this case, the "laser light intensity range used in multiple operation modes" is included in the laser light intensity range in which a large gain can be used, and the gain switching unit 106 switches from a small gain to a large gain so that the gain used in the multiple operation modes of the image forming apparatus 1 is not switched.

[0181] Also, assume that the laser beam intensity range has changed to the "laser beam intensity range used in multiple operation modes" in FIG. 24(b). In this case, the "laser beam intensity range used in multiple operation modes" is included in both the laser beam intensity range in which a medium gain can be used and the laser beam intensity range in which a large gain can be used. Therefore, in order to prevent the gain used by the multiple operation modes of the image forming apparatus 1 from being switched, the gain switching unit 106 can switch from the small gain to the medium gain or the large gain. In this case, the gain switching unit 106 switches to the optimal gain using the same determination process as in FIG. 22. That is, the gain switching unit 106 determines which range the currently set laser beam intensity range falls within. In the example shown in FIG. 24(b), the currently set laser beam intensity range (currently used light intensity range) is included in the laser beam intensity range in which a medium gain can be used, but is not included in the laser beam intensity range in which a large gain can be used. In this case, the gain switching unit 106 switches from the small gain to the medium gain.

[0182] If the gain switching unit 106 makes the above determination and is unable to determine whether the gain should be switched to the medium gain or the large gain, the gain switching unit 106 performs another determination process, as shown in FIG. 22 . Specifically, the gain switching unit 106 determines which of the available light intensity ranges after the gain change will be closest to the center, and switches to the gain corresponding to the available light intensity range that will be closest to the center of the available light intensity range. Here, for a medium gain, the available light intensity range is from Pmin(R1,R2) to Pmax(R1,R2), and for a large gain, the available light intensity range is from Pmin(R1) to Pmax(R1). When the laser light intensity range after the setting change is from Pmin(Now) to Pmax(Now), the gain switching unit 106 switches to the smaller gain of the following equations (23) and (24). The ABS function in equations (23) and (24) returns the absolute value of its argument.

[0183] ABS((Pmax(R1)+Pmin(R1)) / 2-(Pmax(Now)+Pmin(now)) / 2) ···(23) ABS((Pmax(R1,R2)+Pmin(R1,R2)) / 2-(Pmax(Now)+Pmin(now)) / 2) ···(24)

[0184] By using at least one of the above-described determinations, it is possible to minimize the frequency of gain switching, and therefore the frequency of performing color misregistration correction, and reduce the decrease in productivity of the image forming apparatus 1. These determination processes are executed in step S38 shown in FIG. 17 above.

[0185] In each of the above-described embodiments, 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 each of the above-described embodiments, 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 each of the above-described embodiments, 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 downloaded via the network. In each of the above-described embodiments, 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 each of the above-described embodiments, 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.

[0186] The aspects of the present invention are as follows. <1> 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 photodetector element that detects light emitted from the light-emitting element in order to determine a write 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 photodetector element to detect the light; a control unit including a light emission control unit that controls the amount of light emitted by the light emitting element, and a sensitivity switching unit that switches the sensitivity via the sensitivity switching circuit in accordance with the set amount of light; Equipped with The control unit is an image forming apparatus that determines whether to perform color misregistration correction based on the deviation of the writing start timing when the sensitivity is switched by the sensitivity switching unit. <2> The control unit determines not to perform the color shift correction when the sensitivity switching unit switches the sensitivity from a higher sensitivity to a lower sensitivity. <1> 2. The image forming apparatus according to claim 1, wherein: <3> the control unit determines to execute the color shift correction when the sensitivity is switched from low to high by the sensitivity switching unit; <1> 2. The image forming apparatus according to claim 1, wherein: <4> The sensitivity switching unit When the light amount set for the light emitting element exceeds a first light amount that is the maximum value of a usable light amount range of a high sensitivity, the sensitivity is switched from the high sensitivity to a low sensitivity; When the light amount set for the light emitting element falls below a second light amount which is the minimum value of a usable light amount range of a low sensitivity, the sensitivity is switched from the low sensitivity to the high sensitivity. <1> ~ <3> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <5> the sensitivity switching circuit has a first sensitivity and a second sensitivity that is smaller than the first sensitivity as switchable sensitivities; the first light amount is substantially equal to the light amount obtained by multiplying the maximum light amount used in the image forming apparatus by the second sensitivity and dividing the result by the first sensitivity; <4> 2. The image forming apparatus according to claim 1, wherein: <6> the image forming apparatus has a plurality of operation modes each using a different light amount of the light emitting element, the sensitivity switching circuit is set so that there is at least one sensitivity that does not need to be switched when the image forming apparatus operates in the plurality of operation modes; <1> ~ <5> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <7> the sensitivity switching unit switches to a sensitivity that does not need to be switched when the image forming apparatus operates in the plurality of operation modes. <6> 2. The image forming apparatus according to claim 1, wherein: <8> the image forming apparatus has a plurality of operation modes each using a different light amount of the light emitting element, a combination of the first sensitivity and the second sensitivity is set so that a value obtained by multiplying a value obtained by dividing a maximum light amount used in the image forming apparatus by a minimum light amount that can be used when detected at the second sensitivity by the square of a value obtained by dividing the second sensitivity by the first sensitivity is greater than a ratio of a maximum light amount to a minimum light amount used in the plurality of operation modes; <5> 2. The image forming apparatus according to claim 1, wherein: <9> the sensitivity switching circuit has three or more switchable sensitivities, the sensitivity switching unit, when there is a sensitivity that can detect both the light intensity of the light emitting element before the setting is changed and the light intensity of the light emitting element after the setting is changed, switches to the sensitivity when the setting of the light emitting element is changed. <1> ~ <8> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <10> When there is no sensitivity that can detect both the light amount of the light emitting element before the setting change and the light amount of the light emitting element after the setting change, the sensitivity switching unit determines which of the light amount ranges that can be used for each of the sensitivities the light amount of the light emitting element after the setting change will be closest to the center, and switches to the sensitivity corresponding to the light amount range in which the light amount is closest to the center. <9> 2. The image forming apparatus according to claim 1, wherein: <11> the control unit determines whether or not the shift in the writing start timing caused by the switching of the sensitivity is within an allowable range, and if it is within the allowable range, does not perform the color shift correction, and if it is outside the allowable range, performs the color shift correction. <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 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> ~ <11> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <13> the sensitivity switching circuit has, as switchable sensitivities, a third sensitivity, a fourth sensitivity that is smaller than the third sensitivity, and a fifth sensitivity that is smaller than the fourth sensitivity; the ratio of the fourth sensitivity to the third sensitivity is the same as the ratio of the fifth sensitivity to the fourth sensitivity; <1> ~ <3> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. [Explanation of symbols]

[0187] 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 section 92, 92a 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 111 Reference value storage unit 112 Correction value storage unit 113 Gain switching memory unit R1, R2, R3 resistance SW, SW1, SW2 switching elements [Prior art documents] [Patent documents]

[0188] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-303807

Claims

1. 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 photodetector element that detects light emitted from the light-emitting element in order to determine a write 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 photodetector element to detect the light; a control unit including a light emission control unit that controls the amount of light emitted by the light emitting element, and a sensitivity switching unit that switches the sensitivity via the sensitivity switching circuit in accordance with the set amount of light; Equipped with The control unit determines whether to perform color misregistration correction based on the deviation in the writing start timing when the sensitivity switching unit switches the sensitivity.

2. The image forming apparatus according to claim 1 , wherein the control unit determines not to perform the color misregistration correction when the sensitivity switching unit switches the sensitivity from a higher sensitivity to a lower sensitivity.

3. The image forming apparatus according to claim 1 , wherein the control unit determines to perform the color misregistration correction when the sensitivity switching unit switches the sensitivity from low to high.

4. The sensitivity switching unit When the light amount set for the light emitting element exceeds a first light amount that is a maximum value in a usable light amount range of a high sensitivity, the high sensitivity is switched to a low sensitivity; An image forming apparatus according to any one of claims 1 to 3, wherein when the light intensity set for the light-emitting element falls below a second light intensity, which is the minimum value of the usable light intensity range for low sensitivity, the sensitivity is switched from low sensitivity to high sensitivity.

5. the sensitivity switching circuit has a first sensitivity and a second sensitivity that is smaller than the first sensitivity as switchable sensitivities; 5. The image forming apparatus according to claim 4, wherein the first light amount is substantially equal to a light amount obtained by multiplying a maximum light amount used in the image forming apparatus by the second sensitivity and dividing the product by the first sensitivity.

6. the image forming apparatus has a plurality of operation modes each using a different light amount of the light emitting element, An image forming apparatus according to any one of claims 1 to 3, wherein the sensitivity switching circuit is set so that there is at least one sensitivity that does not need to be switched when the image forming apparatus operates in the multiple operating modes.

7. The image forming apparatus according to claim 6 , wherein the sensitivity switching unit switches to a sensitivity that does not need to be switched when the image forming apparatus operates in the plurality of operation modes.

8. the image forming apparatus has a plurality of operation modes each using a different light amount of the light emitting element, 6. The image forming apparatus according to claim 5, wherein the combination of the first sensitivity and the second sensitivity is set so that the value obtained by multiplying the value obtained by dividing the maximum light amount used in the image forming apparatus by the minimum light amount usable when detected at the second sensitivity by the square of the value obtained by dividing the second sensitivity by the first sensitivity is greater than the ratio of the maximum light amount to the minimum light amount used in the multiple operating modes.

9. the sensitivity switching circuit has three or more switchable sensitivities, An image forming apparatus according to any one of claims 1 to 3, wherein the sensitivity switching unit switches to a sensitivity that can detect both the light intensity of the light-emitting element before the setting is changed and the light intensity of the light-emitting element after the setting is changed when the setting of the light-emitting element is changed.

10. The image forming apparatus of claim 9, wherein, when there is no sensitivity that can detect either the light intensity of the light-emitting element before the setting is changed or the light intensity of the light-emitting element after the setting is changed, the sensitivity switching unit determines which of the light intensity ranges that the light intensity of the light-emitting element after the setting is changed will be closest to the center of, among the light intensity ranges that can be used for each of the sensitivities, and switches to the sensitivity corresponding to the light intensity range that is closest to the center.

11. The control unit determines whether the shift in the writing start timing caused by switching the sensitivity is within an acceptable range, and if it is within the acceptable range, does not perform the color shift correction, and if it is outside the acceptable range, performs the color shift correction.

12. The image forming apparatus according to any one of claims 1 to 3, 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.

13. the sensitivity switching circuit has, as switchable sensitivities, a third sensitivity, a fourth sensitivity that is lower than the third sensitivity, and a fifth sensitivity that is lower than the fourth sensitivity, 4. The image forming apparatus according to claim 1, wherein a ratio of the fourth sensitivity to the third sensitivity and a ratio of the fifth sensitivity to the fourth sensitivity are substantially the same.

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