Image forming apparatus

Abstract

To provide an image forming apparatus capable of surely detecting synchronization without causing erroneous detection due to stray light and detection omission due to insufficient light quantity even when the light quantity of a laser beam made incident on a synchronization detection sensor is fluctuated by a printing condition or the like.SOLUTION: According to an aspect of the present invention, there is provided an image forming apparatus that forms an image by developing an electrostatic latent image formed on a photosensitive member with a developer, the image forming apparatus including: a light emission control element that outputs a light emission control signal for controlling a lighting state of a light emitting element to control light emission of the light emitting element; a synchronization detection element that detects a writing start timing of an electrostatic latent image by irradiation of light onto the photosensitive member; a gain switching circuit that can switch a gain of the synchronization detection element; and a gain control signal selection circuit that is connected to the light emission control signal and selects one of a plurality of gain control signals for setting the gain of the synchronization detection element based on the light emission control signal.SELECTED DRAWING: Figure 1-1

Description

[Technical Field]

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

[0002] In an electrophotographic image forming apparatus that exposes a photosensitive member to a light-emitting element such as a laser diode (LD), the beam output from the LD is reflected by a rotating polygon mirror. In an electrophotographic image forming apparatus, when the LD beam (laser beam) 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 on the photosensitive member. At this time, an electrostatic latent image of one line can be formed on the photosensitive member by switching the LD on or off according to input image data. Then, the electrophotographic image forming apparatus can form an electrostatic latent image of the desired image by repeating line scanning while rotating the photosensitive member.

[0003] When the laser beam repeatedly scans one line on the photosensitive drum, it is necessary to synchronize the write start timing for starting image formation.To determine this write start timing, a light detection sensor is installed just before scanning the photosensitive drum to detect the scanning position of the laser beam.This light detection sensor is called a synchronous detection sensor, and the write start timing for image data is determined according to the output signal of the synchronous detection sensor.

[0004] Here, the light detection sensor is a photodiode that uses an amplifier and gain resistor to detect minute changes in current. The presence or absence of a laser beam input can be determined based on these changes in current. Light detection sensors can be made into circuits by combining elements, but photo ICs with slits and cover glass to improve and stabilize detection accuracy are commercially available and can be used inexpensively.

[0005] For example, Patent Document 1 discloses a configuration in which the gain of a synchronous detection circuit is switched by an external signal according to the set light amount for each condition, in order to prevent missed detection and false detection when the light amount fluctuates. Summary of the Invention [Problem to be solved by the invention]

[0006] The light intensity of the laser beam changes depending on the image-making conditions. The image-making conditions include not only changes in the resolution of the output image, but also changes in productivity (e.g., linear speed) and temperature environment. This changes the light intensity of the laser beam input to the synchronous detection sensor. When the light intensity of the laser beam changes, there is a possibility of false detection due to stray light or missed detection due to insufficient light intensity. Furthermore, the configuration described in Patent Document 1 cannot select the optimal gain for each color when a single synchronous detection signal contains synchronization timings for multiple colors.

[0007] The present invention has been made in consideration of the above, and aims to provide an image forming apparatus that can reliably detect synchronization without causing erroneous detection due to stray light or missed detection due to insufficient light, even if the light amount of the laser beam incident on the synchronization detection element varies depending on printing conditions, etc. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the object, the present invention provides an image forming apparatus that forms an image by developing a developer on an electrostatic latent image formed on a photosensitive member, the apparatus comprising an optical writing device that exposes the photosensitive member, the optical writing device including a light emitting element that irradiates the photosensitive member with light, a light emission control element that outputs a light emission control signal that controls the lighting state of the light emitting element to control the light emission of the light emitting element, a multi-faceted reflector that is provided on an optical path of light emitted from the light emitting element and that is rotated to deflect the light irradiated onto the surface of the reflector and scan the photosensitive member in one direction, and a deflection element that deflects the light irradiated onto the surface of the reflector to scan the photosensitive member in one direction, the electrostatic latent image formed on the photosensitive member being different from the light emitting element. a synchronous detection element that is irradiated with light from light-emitting elements of a first color among the plurality of light-emitting elements used to form an electrostatic latent image, and light from light-emitting elements of a second color different from the first color among the plurality of light-emitting elements, and that detects the timing at which writing of an electrostatic latent image by irradiating light onto the photosensitive member starts; a gain switching circuit that can switch the gain of the synchronous detection element; and a gain control signal selection circuit that is connected to the light-emitting control signal and that selects, based on the light-emitting control signal, one of a plurality of gain control signals that are connected to the gain switching circuit of the same synchronous detection element and that set the gain of the synchronous detection element. [Effects of the Invention]

[0009] According to the present invention, even if the amount of light of the laser beam incident on the synchronization detection element varies depending on printing conditions, etc., false detection due to stray light and missed detection due to insufficient light amount do not occur, and synchronization can be reliably detected. [Brief explanation of the drawings]

[0010] [Figure 1-1] FIG. 1A is a diagram for explaining a drop in the amount of light at both ends of a photosensitive member when the light amount of a light emitting element is controlled to be constant in an image forming apparatus according to this embodiment. [Figure 1-2] FIG. 1-2 is a diagram for explaining a drop in the amount of light at both ends of the photosensitive member when the light amount of the light emitting element is controlled to be constant in the image forming apparatus according to the present embodiment. [Figure 2]FIG. 2 is a diagram for explaining an example of a gain selection operation based on a synchronous lighting signal of the image forming apparatus according to the present embodiment. [Figure 3] FIG. 3 is a diagram for explaining an example of a gain selection operation based on an APC signal in the image forming apparatus according to the present embodiment. [Figure 4] FIG. 4 is a diagram for explaining an example of the waveform of a synchronous detection signal when the LD for each image-forming color in the image forming apparatus according to this embodiment has a plurality of light-emitting elements. [Figure 5] FIG. 5 is a diagram for explaining an example of the board layout of the light emission control IC and the gain control signal selection circuit of the image forming apparatus according to the present embodiment. [Figure 6] FIG. 6 is a diagram for explaining an example of the initialization function of the gain control signal selection circuit in the image forming apparatus according to the present embodiment. [Figure 7] FIG. 7 is a diagram illustrating another example of the initialization function of the gain control signal selection circuit in the image forming apparatus according to the present embodiment. [Figure 8] FIG. 8 is a diagram for explaining an example of the operation timing of the initialization signal of the gain control signal selection circuit in the image forming apparatus according to the present embodiment. [Figure 9] FIG. 9 is a diagram illustrating an example of a configuration having a system for updating a characteristic value of a deviation in the timing of starting writing in the image forming apparatus according to the present embodiment. [Figure 10] FIG. 10 is a diagram for explaining another configuration having a system for updating the characteristic value of the deviation in the writing start timing in the image forming apparatus according to the present embodiment. [Figure 11-1] FIG. 11A is a flowchart illustrating an example of the density adjustment operation of the image forming apparatus according to the present embodiment. [Figure 11-2] FIG. 11B is a flowchart illustrating an example of the printing operation of the image forming apparatus according to the present embodiment. [Figure 12-1] FIG. 12A is a flowchart illustrating an example of the color matching operation of the image forming apparatus according to the present embodiment. [Figure 12-2] FIG. 12B is a flowchart illustrating another example of the printing operation of the image forming apparatus according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image forming apparatus will be described in detail below with reference to the accompanying drawings.

[0012] 1-1 and 1-2 are diagrams for explaining the drop in light intensity at both ends of the photosensitive member when the light intensity of the light-emitting element is controlled to be constant in the image forming apparatus according to the present embodiment. In Fig. 1-2, the vertical axis represents the light intensity of the beam emitted from the LD (light-emitting element) or the light intensity of the beam reaching the photosensitive member 106, and the horizontal axis represents the scanning position of the beam on the photosensitive member 106.

[0013] The image forming apparatus according to the present embodiment is an example of an image forming apparatus (e.g., an electrophotographic color image forming apparatus) that forms an image by developing an electrostatic latent image formed on a photoconductor 106 with a developer. The image forming apparatus according to the present embodiment also includes an optical writing device 1 that exposes the photoconductor 106 to light. The optical writing device 1 includes a light-emitting element, an emission control IC 102 (see FIG. 2), a deflection element 103, a synchronization detection IC 104, and a gain switching circuit 104a (see FIG. 10). The light-emitting element is an example of a light-emitting element that irradiates the photoconductor 106 with light. The optical writing device 1 may include multiple light-emitting elements. The emission control IC 102 is an example of an emission control element that outputs an emission control signal that controls the lighting state of the light-emitting element to control the emission of the light-emitting element. The deflection element 103 is a multifaceted reflector that is disposed on the optical path of light emitted from the light-emitting element and is rotated to deflect the light irradiated on the reflector surface to scan the photoconductor 106 in one direction. The synchronous detection IC 104 is an example of a synchronous detection element that detects the start timing of writing an electrostatic latent image by irradiating light onto the photoconductor 106. Furthermore, the synchronous detection IC 104 (the same synchronous detection IC) is irradiated with light from light-emitting elements of a first color among a plurality of light-emitting elements used to form electrostatic latent images on different photoconductors 106, and light from light-emitting elements of a second color different from the first color among the plurality of light-emitting elements. In other words, the synchronous detection IC is irradiated with multiple light beams from the multiple light-emitting elements via different optical paths. Here, the "different optical paths" refer to laser beams different from those in a configuration in which two laser beams are irradiated onto the first color (one photoconductor 106). The "optical path" refers to the optical path to the synchronous detection IC 104. The gain switching circuit 104a is an example of a gain switching circuit that can switch the gain of the synchronous detection IC 104.

[0014] When forming an electrostatic latent image on the photoconductor 106, the optical system 107 exhibits a characteristic phenomenon in which the amount of light reaching the light-emitting element decreases with increasing distance from the center of the photoconductor 106. To correct this decrease in light amount, a driver with a correction function that increases the amount of light emitted from the light-emitting element at both ends is known. Using this correction function would allow the amount of light incident on the synchronous detection plate (synchronous detection IC 104) to be constant regardless of conditions, but this increases costs. Therefore, in this embodiment, a driver with constant light amount control without a correction function is used to achieve an inexpensive configuration. Specifically, the light emission control IC 102 controls the light amount of the light-emitting element to be constant while the light irradiated from one end of the deflection element 103 scans in one direction from one end to the other. This allows for an inexpensive system without shading correction.

[0015] 2 is a diagram for explaining an example of a gain selection operation based on a synchronous lighting signal of the image forming apparatus according to this embodiment. In this embodiment, the image forming apparatus includes a light emission control IC 102, a CPU (Central Processing Unit) 201, a gain control signal selection circuit 202, a synchronous detection IC 104, etc.

[0016] The light emission control IC 102 outputs a synchronous lighting signal (an example of a light emission control signal) that controls the lighting state of the light-emitting element. The CPU 201 is connected to the gain switching circuit 104a of the synchronous detection IC 104 and outputs a gain signal (an example of a gain control signal) that sets the gain of the synchronous detection IC 104. The CPU 201 also outputs multiple gain signals suited to each of the multiple light-emitting elements. The gain control signal selection circuit 202 is an example of a gain control signal selection circuit that selects a gain selection signal, which is one of the multiple gain signals connected to the gain switching circuit 104a of the same synchronous detection IC 104. The gain control signal selection circuit 202 is also connected to the synchronous lighting signal output from the light emission control IC 102. That is, the gain control signal selection circuit 202 selects a gain selection signal, which is one of the multiple gain signals, based on the synchronous lighting signal (an example of a light emission control signal) output from the light emission control IC 102. This enables appropriate synchronous detection even when laser beams with different powers are incident on a single synchronous detection IC 104, i.e., it is possible to suppress stray light and detection omissions.

[0017] The example shown in FIG. 2 is a system in which two color beams, black and yellow, are synchronized using a single synchronization detection IC 104. The synchronization signal for each color is asserted before and after the laser beam of each color scans the synchronization detection IC 104. This timing coincides with the timing for selecting the gain signal, so it is reasonable to use the synchronization signal, among the light emission control signals, as the gain control signal. In other words, the gain control signal selection circuit 202 may be connected to the synchronization signal among the light emission control signals (i.e., the synchronization signal may be input). Alternatively, the gain control signal selection circuit 202 may be connected to (input to) a single-ended signal among the light emission control signals.

[0018] FIG. 3 is a diagram illustrating an example of a gain selection operation using an APC signal in an image forming apparatus according to this embodiment. In this embodiment, the synchronized lighting signal is also used as a data signal, and when it cannot be connected to the gain control signal selection circuit 202 (i.e., when the synchronized lighting signal is not input to the gain control signal selection circuit 202), the APC signal is used instead. Because the synchronized lighting timing (the timing when the synchronized lighting signal is asserted) is the gain selection timing, the APC signal can be used as a gain switching signal by performing APC control so that it overlaps with the synchronized lighting timing (it does not need to overlap completely). In other words, the gain control signal selection circuit 202 is connected to the APC signal (i.e., the APC signal is input) among the light emission control signals. Because the APC signal is asserted near the synchronized lighting, it is suitable for switching the gain signal. Furthermore, the timing when the APC signal operates may overlap with the synchronized lighting timing.

[0019] FIG. 4 is a diagram illustrating an example of the waveform of a synchronous detection signal when the LD for each image-forming color in the image forming apparatus according to this embodiment has multiple light-emitting elements. FIG. 4 is a diagram illustrating an example in which two laser beams of two colors enter one synchronous detection plate (synchronous detection IC 104), and each laser beam has two light-emitting elements. Since the amount of light required for image formation is common among light-emitting elements of the same color, an increase in circuit area can be suppressed by sharing a gain signal. That is, when the optical writing device 1 has multiple light-emitting elements that irradiate one photosensitive element 106, the multiple light-emitting elements share a synchronous detection signal. That is, the light-emission control IC 102 outputs a light-emission control signal based on one of the synchronous detection signals from the synchronous detection IC 104. This allows light-emitting elements of the same color to share a synchronous detection signal, thereby reducing the circuit area.

[0020] 5 is a diagram illustrating an example of the board layout of the light emission control IC and gain control signal selection circuit of the image forming apparatus according to this embodiment. Generally, the control board 2 and the optical writing device 1 are arranged separately within the image forming apparatus, and may be electrically connected by a harness. Because the harness is susceptible to the influence of external noise, the influence of noise can be reduced by arranging the gain control signal selection circuit 202 and the light emission control IC 102 on the same board. Furthermore, when multiple synchronization detection plates (synchronization detection ICs 104) and laser drive boards 108 are mounted within the optical writing device 1, the number of electrical wires can be reduced.

[0021] FIG. 6 is a diagram illustrating an example of an initialization function of the gain control signal selection circuit in the image forming apparatus according to the present embodiment. The gain control signal selection circuit 202 has an initialization function (CLR terminal in FIG. 6) that initializes the state of the gain control signal selection circuit 202. Specifically, the gain control signal selection circuit 202 includes a D flip-flop (an example of a flip-flop) and a NAND gate. This allows the state of the gain selection signal to be maintained. When the CLR signal of the D flip-flop changes to low level, the gain selection signal is reset to its initial state accordingly, and the gain selection signal supplied to the synchronous detection IC 104 is initialized. An initialization signal (gain selection initialization signal) that enables or disables the initialization function is output from the light emission control IC 102, which generates the light emission control signal. This initializes the state of the gain selection signal for each line, preventing discrepancies between the gain selection signal and the corresponding color of light incident on the synchronous detection IC 104. The gain control signal selection circuit 202 is not limited to a logic IC such as a D flip-flop or a NAND gate, as long as it has a function of switching the gain selection signal.

[0022] In this embodiment, a light emission control signal that controls the light emission of an LD (light emitting element) on an LDB (laser driving board) is branched and connected. One signal output from the light emission control IC 102 controls the light emission of the LD (light emitting element) on the LDB and also controls a gain selection initialization circuit (gain control signal selection circuit 202).

[0023] However, branching and connecting an LVDS signal (differential signal) as an initialization signal has drawbacks, such as increased circuit load, waveform distortion, signal quality degradation, and unwanted radiation. LVDS signals are also used for high-speed transmission signals such as data signals (signals that turn LDs on or off according to the image in the image area), and there is a concern that connecting them to data signals could adversely affect the image itself. To prevent such adverse effects, it is desirable to branch a single-ended signal from the light emission control signal and connect it as an initialization signal (gain selection initialization signal). In other words, the single-ended signal from the light emission control signal can be used as the initialization signal. This reduces the impact on waveform quality and EMI compared to using an LVDS signal as the initialization signal.

[0024] FIG. 7 is a diagram illustrating another example of the initialization function of the gain control signal selection circuit in the image forming apparatus according to the present embodiment. The configuration of the image forming apparatus shown in FIG. 7 differs from the configuration of the image forming apparatus shown in FIG. 6 in that the gain selection initialization signal output from the light emission control IC 102 is connected to the gain control signal selection circuit 202 independently of the light emission control signal that controls the light emission of the LD (light emitting element) on the LDB. In other words, the gain selection initialization signal may be connected to the light emission control IC 102 independently of the light emission control signal that controls the lighting state of the light emitting element. This eliminates the need for a new generation circuit by using an unused terminal of the light emission control IC 102. Whether the signals are connected in a branched manner or independently, the initialization state is controlled by the light emission control IC 102 in both cases.

[0025] A notable feature of the configuration of the image forming apparatus shown in Figure 7 is that the gain selection signal can be initialized by the gain selection initialization signal at a desired timing. The light emission control IC 102 operates in synchronization with the synchronous detection signal input from the synchronous detection IC 104, so it generates the gain selection initialization signal in accordance with the operation cycle, thereby initializing the gain selection signal. The initialization timing can then be adjusted to the desired timing in the operation cycle.

[0026] Fig. 8 is a diagram for explaining an example of the operation timing of the initialization signal of the gain control signal selection circuit in the image forming apparatus according to this embodiment. In this embodiment, in the configuration of the image forming apparatus shown in Fig. 7, the generation timing of the gain selection initialization signal can be adjusted independently of the light emission control signal (for example, the synchronous detection signal). The gain selection initialization signal can be generated at any timing once during the period from when the synchronous detection signal is asserted (=Low) to when it is asserted again (=Low).

[0027] Initializing the gain selection signal means returning the optical system (light detection sensor 104b on the synchronous detection IC 104) to a state where a synchronous detection signal is appropriately generated by the leading synchronous lighting signal (Bk in FIG. 8). In other words, in this embodiment, it means transitioning the state of the gain selection signal so that the Bk gain selection signal is output. In this case, the gain selection signal must be initialized before the leading Bk synchronous lighting signal is generated.

[0028] At the same time, the gain selection signal must be switched so that the synchronous detection signal is generated appropriately by the final synchronous lighting signal (Ye in Figure 8). In other words, the gain selection signal must be initialized after the final Ye synchronous lighting signal has finished. If the gain selection signal is initialized at a timing between the above two, it becomes possible to initialize the ideal gain signal.

[0029] That is, when a latent image for one scan is formed on each of the different photoconductors 106 by rotationally driving the deflection element 103, and the photoconductor 106 on which a latent image is formed first on the time axis is referred to as the leading photoconductor 106, and the photoconductor 106 on which a latent image is formed last is referred to as the trailing photoconductor 106, the initialization function operates between the detection of the synchronous lighting signal for the trailing photoconductor 106 and the detection of the synchronous lighting signal for the leading photoconductor 106. As a result, by performing initialization at the appropriate timing, malfunctions can be prevented.

[0030] 9 is a diagram illustrating an example of a configuration having a system for updating a characteristic value of a deviation in the write start timing in an image forming apparatus according to this embodiment. The gain switching circuit 104a of the synchronization detection IC 104 includes at least two gain signals (SIG1 and SIG2 in FIG. 9). One of the gain signals operates so that the gain is switched depending on the behavior of the light emission control IC 102. The other gain signal is connected to a circuit that is not affected by the behavior of the light emission control IC 102.

[0031] The light-emission control IC 102 is a circuit that repeatedly operates according to the synchronous detection period. Therefore, the other gain signal (SIG1 in FIG. 9) does not operate according to the period of the synchronous detection signal, and therefore does not need to operate according to the period of the synchronous detection signal. For example, the other gain signal (SIG1 in FIG. 9) may be used to measure the amount of deviation in detection timing when the amount of light irradiated on the light detection sensor 104b of the synchronous detection IC 104 changes. The detection timing of the light detection sensor 104b is measured when the other gain signal (SIG1 in FIG. 9) is fixed to a low level and a Bk or Ye gain signal (SIG2 in FIG. 9) is set, and the detection timing of the light detection sensor 104b is measured when the other gain signal (SIG1 in FIG. 9) is fixed to a high level and a Bk or Ye gain signal (SIG2 in FIG. 9) is set. From the results, a characteristic value of the deviation in detection timing when the amount of light incident on the light detection sensor 104b changes is calculated. Then, a correction amount is calculated from the calculated characteristic value of the deviation in detection timing. In this way, in order to correct the deviation in detection timing, at least one of the plurality of gain signals is configured to be connected to a circuit other than the light emission control IC 102.

[0032] That is, when a system that updates the characteristic value of the deviation in the timing at which an image is written due to gain switching is operating, the gain signals connected to circuits other than the gain control signal selection circuit 202 are operating, and when other systems are operating, the logic of the gain signals connected to circuits other than the gain control signal selection circuit 202 is fixed. This makes it possible to provide high-quality images.

[0033] 10 is a diagram illustrating another configuration of an image forming apparatus according to this embodiment, which includes a system for updating a characteristic value of a deviation in the write start timing. In this embodiment, the gain switching circuit 104a of the synchronization detection plate (synchronization detection IC 104) includes at least two gain signals (SIG1 and SIG2 in FIG. 10), and one of the gain switching signals may operate to switch the gain depending on the behavior of the light emission control IC 102. The other gain signal is connected to a circuit that is not affected by the behavior of the light emission control IC 102.

[0034] The gain switching circuit 104a is realized, for example, by a combination of resistors and transistors. If the gain resistors R1, R2, and R3 are 3.0 kΩ, 10.0 kΩ, and 5.10 kΩ, respectively, and the gain ratio is 1.30 or 0.69, the gain resistor values ​​can be set to four values ​​depending on whether the transistors are ON or OFF: 3.0 kΩ, 2.31 kΩ, 1.89 kΩ, and 1.59 kΩ. Assume, for example, that 2.31 kΩ and 1.59 kΩ are used in printing. When used in printing, the light emission control IC 102 must be able to appropriately switch the Bk or Ye gain, so 2.31 kΩ and 1.59 kΩ must be selectable by the Bk or Ye gain signal. 10, when SIG1 is ON and SIG2 is OFF, the resistance is 2.31 kΩ, and when SIG1 is ON and SIG2 is ON, the resistance is 1.59 kΩ, so SIG2 is the signal connected to the light emission control IC 102. SIG1 is not connected to the light emission control IC 102, but is connected to, for example, the engine CPU, and its output is switched between low and high levels when an update system that updates the characteristic value of the detection timing deviation of the light detection sensor 104b is operated. During printing, SIG1 is always maintained in the ON state (= high level).

[0035] With this configuration, a system can be constructed in which the light emission control IC 102 and the gain control signal selection circuit 202 can appropriately switch between the Bk and Ye gain signals during printing, while at the same time updating the characteristic value of the detection timing deviation of the light detection sensor 104b. In other words, there are multiple gain signals for setting the gain of the synchronization detection IC 104, and at least one of these is connected to a circuit other than the gain control signal selection circuit 202. This makes it possible to select between a gain to be used in printing and a gain not to be used in printing.

[0036] 11A and 11B are flowcharts illustrating an example of a density adjustment operation of the image forming apparatus according to the present embodiment, and a printing operation of the image forming apparatus according to the present embodiment.

[0037] In the density adjustment operation shown in FIG. 11-1, the light intensity of the laser beam, which is one of the image formation conditions, is adjusted. Specifically, the image forming apparatus executes pre-detection processing of the light intensity of the laser beam (step S1101). Next, the image forming apparatus forms a density adjustment pattern (step S1102). Next, the synchronization detection IC 104 detects the density adjustment pattern (step S1103), and calculates the light intensity of the LD (light emitting element) based on the detection result (step S1104).

[0038] If the light intensity of the laser beam changes, the light intensity of the laser beam incident on the light detection sensor 104b of the synchronous detection IC 104 also changes, so it is necessary to determine whether or not the gain of the synchronous detection IC 102 needs to be switched. Therefore, the image forming apparatus determines whether the calculation result of the light intensity of the LD (light emitting element) is a normal value (step S1105). If the light intensity of the LD is a normal value (step S1105: Yes), the image forming apparatus updates the set value of the light intensity of the LD (step S1106). Then, if it is determined that gain switching is necessary (step S1107: Yes), the image forming apparatus updates the set value of the gain of the synchronous detection IC 104 (gain set value) stored in a storage unit such as a memory (step S1108).

[0039] At this time, since there are as many gain setting values ​​stored in the memory as there are laser beams incident on the light detection sensor 104b, the gain setting values ​​stored in the memory are updated to match the laser beams whose light intensity has been adjusted by the density adjustment operation. The updated gain setting values ​​are reflected when a printing operation or adjustment operation is performed.

[0040] In the printing operation shown in FIG. 11-2, the image forming apparatus first sets the sensitivity of the optical detection sensor 104b (step S1109) and then executes pre-printing process (step S1110). Setting the sensitivity of the optical detection sensor 104b involves reading a gain setting value stored in a memory unit and setting the gain of the optical detection sensor 104b to an appropriate value. At this time, the gain setting values ​​for a single color are read for monochrome operation, and for all colors are read for full-color operation. In this way, appropriate gain setting values ​​are set to match the laser beams corresponding to the adjusted light intensities of the colors. The pre-printing process also includes polygon mirror rotation control and settings for the light emission control IC 102 and the laser drive circuit board 108 required to light the LD. After the pre-printing process, the image forming apparatus initializes the LD (step S1111).

[0041] When the LD is successfully initialized (step S1112: Yes), the image forming apparatus waits for detection of a synchronization detection signal (step S1113). When the laser beams corresponding to the respective colors are sequentially incident on the light detection sensor 104b, the hardware gain control signal selection circuit 202 outputs an appropriate gain signal in accordance with the respective synchronized lighting timings. When the light detection sensor 104b successfully detects the laser beam and the image forming apparatus detects a synchronization detection signal (step S1113: Yes), the image forming apparatus adjusts the write start timing (step S1114) and executes processing during the printing operation (step S1115). After that, when all print jobs are completed (step S1116: Yes), the image forming apparatus executes post-printing operation processing (step S1117). On the other hand, when the LD cannot be successfully initialized (step S1112: No) or when the synchronization detection signal cannot be detected (step S1113: No), the image forming apparatus executes a forced termination process for the printing operation (step S1118).

[0042] 12A and 12B are flowcharts illustrating an example of a color matching operation of the image forming apparatus according to the present embodiment, and another example of a printing operation of the image forming apparatus according to the present embodiment.

[0043] In the color matching operation shown in FIG. 12-1, the image forming apparatus sets the sensitivity of the optical detection sensor 104b of the synchronous detection IC 104 (step S1201) and then performs pre-detection processing (step S1202). Then, the image forming apparatus forms a color matching pattern (step S1203) and detects the color matching pattern (step S1204). If the color matching pattern is successfully detected (step S1205: Yes), the image forming apparatus calculates a correction value (step S1206).

[0044] If the calculated correction value is normal (step S1207: Yes), the image forming apparatus updates the color matching correction amount (step S1208) and updates the color matching execution conditions (step S1209). In this embodiment, in order to correct the writing start timing shown in Figures 9 and 10, the light intensity of the laser beam during the color matching operation is stored in a storage unit such as a memory when the color matching execution conditions are updated (step S1209). The image forming apparatus shown in Figures 9 and 10 is equipped with an update system for the color matching correction amount and the color matching execution conditions, but this update system may be provided external to the image forming apparatus.

[0045] In the printing operation shown in FIG. 12-2, the image forming apparatus first sets the sensitivity of the light detection sensor 104b (step S1210) and executes pre-printing process (step S1211). Next, the image forming apparatus initializes the LD (step S1212). If the LD is successfully initialized (step S1213: Yes) and a synchronization detection signal is detected (step S1214: Yes), the image forming apparatus reads the execution conditions for color matching during the printing operation (e.g., the light intensity stored in the memory unit) (step S1215). Next, the image forming apparatus adjusts the write start timing (step S1216) and executes processing during the printing operation (step S1217). For example, if there is a difference between the light intensity of the laser beam during the color matching operation and the current light intensity of the laser beam, the detection timing of the light detection sensor 104b will be shifted by that difference. Therefore, the image forming apparatus calculates a correction amount based on the characteristic value of the difference and adjusts the write start timing (step S1216). In this respect, the printing operation shown in FIG. 12-2 differs from the printing operation shown in FIG. 11-2.

[0046] When all print jobs are completed (step S1218: Yes), the image forming apparatus executes post-print operation processing (step S1219). On the other hand, if the LD cannot be properly initialized (step S1213: No) or if the synchronization detection signal cannot be detected (step S1214: No), the image forming apparatus executes forced termination processing of the print operation (step S1220).

[0047] In this way, with the image forming apparatus according to this embodiment, even if the amount of light of the laser beam incident on the synchronization detection sensor fluctuates depending on the printing conditions, etc., false detection due to stray light and missed detection due to insufficient light amount do not occur, and synchronization can be reliably detected.

[0048] In the above embodiment, the image forming apparatus of the present invention is described as being applied to a multifunction peripheral having at least two of the functions of a copy function, a printer function, a scanner function, and a facsimile function, but the present invention can be applied to any image forming apparatus such as a copier, printer, scanner device, or facsimile device.

[0049] For example, aspects of the present invention are as follows. <1> An image forming apparatus that forms an image by developing an electrostatic latent image formed on a photosensitive member with a developer, an optical writing device that exposes the photosensitive member; The optical writing device a light emitting element that irradiates the photosensitive member with light; a light-emission control element that outputs a light-emission control signal that controls the lighting state of the light-emitting element to control the light emission of the light-emitting element; a deflection element that is a multi-faceted reflector that is provided on an optical path of light emitted from the light emitting element and that is driven to rotate to deflect the light irradiated onto the surface of the reflector and scan the photosensitive member in one direction; a synchronization detection element that is irradiated with light from light-emitting elements of a first color among the plurality of light-emitting elements used to form the electrostatic latent images on the different photosensitive members, and light from light-emitting elements of a second color different from the first color among the plurality of light-emitting elements, and that detects the timing at which writing of the electrostatic latent images by irradiation of light onto the photosensitive members begins; a gain switching circuit capable of switching the gain of the synchronous detection element; a gain control signal selection circuit connected to the light emission control signal, and selecting one of a plurality of gain control signals connected to the gain switching circuit of the same synchronous detection element and setting a gain of the synchronous detection element based on the light emission control signal; An image forming apparatus comprising: <2> the light emission control element controls the light amount of the light emitting element to be constant while the light irradiated from one end to the other of one surface of the deflection element scans in one direction; <1> 2. The image forming apparatus according to claim 1 . <3> a single-ended signal of the light emission control signal is connected to the gain control signal selection circuit; <1> or <2> 2. The image forming apparatus according to claim 1 . <4> a synchronous lighting signal among the light emission control signals is connected to the gain control signal selection circuit; <1> or <2> 2. The image forming apparatus according to claim 1 . <5> an APC signal among the light emission control signals is connected to the gain control signal selection circuit; <1> or <2> 2. The image forming apparatus according to claim 1 . <6> The timing when the APC signal operates overlaps with the timing when the lights are synchronously turned on. <5> 2. The image forming apparatus according to claim 1 . <7> the optical writing device has a plurality of the light emitting elements for irradiating one of the photosensitive bodies, a plurality of the light emitting elements share a synchronous detection signal from the synchronous detection element; <1> from <5> 10. The image forming apparatus according to claim 9, wherein <8> the gain control signal selection circuit has an initialization function for initializing a state of the gain control signal selection circuit; an initialization signal for setting the initialization function to be enabled or disabled is output from the light-emitting control element; <1> from <7> 10. The image forming apparatus according to claim 9, wherein <9> the initialization signal is connected to the light-emitting control element independently of the light-emitting control signal for controlling the lighting state of the light-emitting element; <8> 2. The image forming apparatus according to claim 1 . <10> A single-ended signal of the light emission control signal is used as an initialization signal. <8> 2. The image forming apparatus according to claim 1 . <11> When a latent image for one scan is formed on each of the different photosensitive members by rotationally driving the deflection element, When the photoconductor on which the latent image is formed first on the time axis is referred to as the leading photoconductor, and the photoconductor on which the latent image is formed last is referred to as the trailing photoconductor, the initialization function is activated during the period from when a synchronous turn-on signal for the rearmost photoconductor is detected until when a synchronous turn-on signal for the leading photoconductor is detected; <9> or <10> 2. The image forming apparatus according to claim 1 . <12> There are a plurality of gain control signals, and at least one of the gain control signals is connected to a circuit other than the gain control signal selection circuit. <1> from <11> 10. The image forming apparatus according to claim 9, wherein <13> When a system that updates a characteristic value of a deviation in the timing at which an image is written due to gain switching of the synchronous detection element operates, the gain control signal connected to a circuit other than the gain control signal selection circuit operates, and when other systems operate, the logic of the gain control signal connected to a circuit other than the gain control signal selection circuit operates to be fixed. <12> 2. The image forming apparatus according to claim 1 . <14> The gain control signal selection circuit and the light emission control element are on the same substrate. <1> from <13> 10. The image forming apparatus according to claim 9, wherein <15> the gain control signal selection circuit includes a flip-flop and a NAND gate; <9> 2. The image forming apparatus according to claim 1 . [Explanation of symbols]

[0050] 1 Optical writing device 102 Light Emitting Control IC 103 Deflection element 104 Synchronous detection IC 104a Gain switching circuit 104b Light detection sensor 106 Photoreceptor 107 Optical system 201 CPU 202 Gain control signal selection circuit [Prior art documents] [Patent documents]

[0051] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-113899

Claims

1. An image forming apparatus that forms an image by developing an electrostatic latent image formed on a photosensitive member with a developer, an optical writing device that exposes the photosensitive member; The optical writing device a light emitting element that irradiates the photosensitive member with light; a light-emission control element that outputs a light-emission control signal that controls the lighting state of the light-emitting element to control the light emission of the light-emitting element; a deflection element that is a multi-faceted reflector that is provided on an optical path of light emitted from the light emitting element and that is driven to rotate to deflect the light irradiated onto the surface of the reflector and scan the photosensitive member in one direction; a synchronization detection element that is irradiated with light from light-emitting elements of a first color among the plurality of light-emitting elements used to form the electrostatic latent images on the different photosensitive members, and light from light-emitting elements of a second color different from the first color among the plurality of light-emitting elements, and that detects the timing at which writing of the electrostatic latent images by irradiation of light onto the photosensitive members starts; a gain switching circuit capable of switching the gain of the synchronous detection element; a gain control signal selection circuit connected to the light emission control signal, and selecting one of a plurality of gain control signals connected to the gain switching circuit of the same synchronous detection element and setting a gain of the synchronous detection element based on the light emission control signal; An image forming apparatus comprising:

2. 2. The image forming apparatus according to claim 1, wherein the light emission control element controls the light amount of the light emitting element to be constant while the light irradiated from one end to the other of one surface of the deflection element scans in one direction.

3. 3. The image forming apparatus according to claim 1, wherein a single-ended signal of the light emission control signal is connected to the gain control signal selection circuit.

4. 3. The image forming apparatus according to claim 1, wherein a synchronous lighting signal of the light emission control signals is connected to the gain control signal selection circuit.

5. 3. The image forming apparatus according to claim 1, wherein an APC signal of the light emission control signals is connected to the gain control signal selection circuit.

6. 6. The image forming apparatus according to claim 5, wherein the timing at which the APC signal is activated coincides with the timing at which synchronized lighting occurs.

7. the optical writing device has a plurality of the light emitting elements for irradiating one of the photosensitive bodies, 2. The image forming apparatus according to claim 1, wherein a plurality of said light emitting elements share a synchronous detection signal from said synchronous detection element.

8. the gain control signal selection circuit has an initialization function for initializing a state of the gain control signal selection circuit; 2. The image forming apparatus according to claim 1, wherein an initialization signal for enabling or disabling the initialization function is output from the light emission control element.

9. 9. The image forming apparatus according to claim 8, wherein the initialization signal is connected to the light emission control element independently of the light emission control signal for controlling the lighting state of the light emitting element.

10. 9. The image forming apparatus according to claim 8, wherein a single-ended signal of the light emission control signal is used as an initialization signal.

11. When a latent image for one scan is formed on each of the different photosensitive members by rotationally driving the deflection element, When the photoconductor on which the latent image is formed first on the time axis is referred to as the leading photoconductor, and the photoconductor on which the latent image is formed last is referred to as the trailing photoconductor, 11. The image forming apparatus according to claim 9, wherein the initialization function operates during a period from when a synchronous turn-on signal for the rearmost photosensitive member is detected until when a synchronous turn-on signal for the leading photosensitive member is detected.

12. 2. The image forming apparatus according to claim 1, wherein there are a plurality of said gain control signals, and at least one of said gain control signals is connected to a circuit other than said gain control signal selection circuit.

13. 13. The image forming apparatus of claim 12, wherein when a system that updates a characteristic value of a deviation in the timing at which an image is written due to gain switching of the synchronous detection element is operating, the gain control signal connected to a circuit other than the gain control signal selection circuit is operating, and when other systems are operating, the logic of the gain control signal connected to a circuit other than the gain control signal selection circuit is fixed.

14. 2. The image forming apparatus according to claim 1, wherein said gain control signal selection circuit and said light emission control element are on the same substrate.

15. 9. The image forming apparatus according to claim 8, wherein the gain control signal selection circuit includes a flip-flop and a NAND gate.

Images