JP6292960B2 - Image forming apparatus - Google Patents

Description

The present invention relates to images forming apparatus provided with a correction means for correcting a color shift and the like.

  Conventionally, an electrophotographic copying method in which an electrostatic latent image is formed on a photoreceptor using laser light emitted from a scanning optical device (laser scanner), and a color image is formed using a toner image obtained by developing the electrostatic latent image. Image forming apparatuses such as printers and printers are widely known.

  Various electrophotographic color image forming apparatuses have been proposed in which a plurality of image forming units are provided to speed up processing, and images of different colors are sequentially transferred onto a conveyance belt or a recording material. Yes. A problem with this type of image forming apparatus is that, for example, the thermal expansion of optical members such as lenses and mirrors is caused by the heat generated by the rotation of a rotary polygon mirror that deflects laser light (light beam) emitted from a laser scanner. As a result, the deformation or the position or posture changes. When the optical member is deformed or changes its position or posture due to thermal expansion, the irradiation position of the light beam on the photosensitive member fluctuates, and the positions when the toner images of the respective colors are superimposed do not match, causing color misregistration. . To solve this problem, a color misregistration detection pattern is formed on the transfer belt at a predetermined timing, the color misregistration amount is detected by reading the pattern with a sensor, and the color misregistration is controlled by controlling the image writing timing according to the detection amount. A technique for correcting the above is known.

  However, such a color misregistration correction technique needs to detect and correct the color misregistration amount by using a color misregistration detection pattern at an appropriate time interval or every number of printed sheets, resulting in an increase in downtime. In response to this problem, the correspondence between the in-machine temperature of the laser scanner and the color misregistration amount is obtained in advance, and the color misregistration amount is predicted based on the in-machine temperature, thereby correcting the color misregistration without forming a color misregistration pattern. The technique which performs is proposed (refer patent document 1 and patent document 2).

  The techniques described in Patent Documents 1 and 2 detect the temperature in the housing of the laser scanner and predict the amount of color misregistration in the sub-scanning direction in which each light beam scans the corresponding photoconductor according to the detected temperature. The scanning timing for scanning one line is corrected based on the predicted color misregistration amount.

JP 2006-11289 A JP 2011-154129 A

  However, in the technique of Patent Document 1, the temperature sensor is arranged at a position away from the polygon motor that is a heat source, and therefore, the temperature rise amount tends to be lower than when the temperature sensor is arranged in the vicinity of the heat source. For this reason, sensitivity at the time of predictive control of color misregistration correction is reduced, and control errors are likely to occur. Further, depending on the configuration of the laser scanner, the temperature sensor may be disposed at a position away from the optical member. In such a case, the temperature rising behavior of the optical member cannot be accurately detected, and the accuracy of predictive control There is a problem that cannot be secured.

  In the technique of Patent Document 2, the correction is performed using the temperature in the vicinity of the rotating polygon mirror and the temperature at other positions in the image forming apparatus to improve the accuracy. When detecting this temperature, it is likely to be affected by the air flow, so there is a risk of performing erroneous prediction control.

The present invention is based on a change in the internal temperature of the device, and to provide an accurate prediction correction control the images forming apparatus that Ru can be executed.

In order to achieve the above object, an image forming apparatus according to the present invention includes a photoconductor, a light source, a rotating polygon mirror that deflects light emitted from the light source, and a driving unit that rotates the rotating polygon mirror . An exposure apparatus that has a housing that houses the light source and the rotating polygon mirror, and that exposes the photosensitive member with light deflected by the rotating polygon mirror to form an electrostatic latent image on the photosensitive member ; A developing unit that develops the electrostatic latent image on the photosensitive member to form an image, a temperature detection unit that is provided inside the housing and detects the temperature of the exposure apparatus, and the rotary polygon mirror rotates. The first temperature is detected by the temperature detection means at a first timing in a state where the rotation is stopped, and the temperature detection means is changed to a second timing before the rotation polygon mirror starts to rotate after the first timing. 2 temperature is detected, the first temperature Determining means for determining the amount of color misregistration on the basis of the second temperature, the exposure timing after said rotating polygon mirror for the exposure apparatus exposing the photoreceptor based on image data starts to rotate, and having a correction means for correcting, based on the color shift amount determined by the determining means.

  According to the present invention, when the internal temperature temporarily decreases with the start of rotation of the rotary polygon mirror, the correction means uses the temperature detected by the temperature detection unit and the reference temperature before the rotation of the rotary polygon mirror starts. Make corrections. Accordingly, erroneous correction based on the apparent temperature change of the internal temperature of the apparatus can be avoided, and accurate predictive correction control can be executed based on the change of the internal temperature.

1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment. FIG. 2 is a perspective view of the scanning optical device applied to the image forming apparatus of FIG. 1 with a lid member removed. It is a top view of the state which removed the cover member in a scanning optical apparatus. It is sectional drawing along the A-A 'line in FIG. 2B. It is a perspective view which shows the main structures of the scanning optical apparatus of FIG. 2A. 3 is a block diagram illustrating a control system of an image forming apparatus including the scanning optical device of FIGS. 2A to 2D. FIG. 3 is a flowchart showing a procedure of image forming processing by an image forming apparatus to which the scanning optical device of FIGS. 2A to 2D is applied. It is a figure which shows the change of the internal temperature of a laser scanner accompanying the rotation start of a polygon mirror. 5 is a flowchart showing a procedure of color misregistration prediction correction control processing in step 106 in FIG. 4. FIG. 3 is a diagram showing a relationship between a temperature rise amount of an internal temperature and a color shift change amount in the scanning optical device of FIG. 2. It is a figure which shows the signal timing of the synchronizing signal and drive signal in the light-emitting device of an optical unit. FIGS. 9A and 9B are diagrams for explaining a scanning optical device equipped with a multi-beam type light source, in which FIG. 9A is a perspective view showing a main configuration, and FIG. FIG. 9C is a diagram showing the imaging position, and FIG. 9C is a diagram showing the beam optical path and the imaging position after the temperature rise. It is a figure which shows the correlation with the variation | change_quantity of the temperature of a scanning optical apparatus, and the variation | change_quantity of the relative dot position between beams.

  Hereinafter, embodiments will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment. This image forming apparatus is a digital full-color printer (color image forming apparatus) that forms an image using toner of a plurality of colors.

  In FIG. 1, an image forming apparatus 100 includes an image forming unit 101Y that forms a yellow image, an image forming unit 101M that forms a magenta image, an image forming unit 101C that forms a cyan image, and an image forming unit 101Bk that forms a black image. It has. Here, Y, M, C, and Bk represent members corresponding to the respective colors of yellow, magenta, cyan, and black. The image forming units 101Y to 101Bk form toner images of corresponding colors using yellow, magenta, cyan, and black toners, respectively.

  Each of the image forming units 101Y to 101Bk includes photosensitive drums 102Y, 102M, 102C, and 102Bk as photoconductors. Around the photosensitive drums 102Y to 102Bk, charging devices 103Y, 103M, 103C, and 103Bk and scanning optical devices (laser scanners) 104Y, 104M, 104C, and 104Bk are provided, respectively. Corresponding to the photosensitive drums 102Y to 102Bk, developing devices 105Y, 105M, 105C, and 105Bk and drum cleaning devices 106Y, 106M, 106C, and 106Bk are arranged, respectively.

  Below the image forming units 101Y to 101Bk, an endless intermediate transfer belt 107 is disposed as an intermediate transfer member. The intermediate transfer belt 107 is stretched around a driving roller 108 and driven rollers 109 and 110, and rotates in the direction of arrow B in the figure during image formation. Primary transfer devices 111Y, 111M, 111C, and 111Bk are provided at positions facing the photosensitive drums 102Y to 102Bk through the intermediate transfer belt 107, respectively. A secondary transfer roller 112 is provided so as to face the driven roller 110 with the intermediate transfer belt 107 interposed therebetween. The secondary transfer roller 112 applies a transfer bias to transfer the toner image on the intermediate transfer belt 107 to a sheet S as a recording medium. Below the intermediate transfer belt 107, a sheet feeding cassette 115 for accommodating the sheet S and a manual feeding cassette 114 are arranged. The sheet S accommodated in the sheet feeding cassette 115 and the manual feeding cassette 114 is supplied to the secondary transfer portion where the driven roller 110 and the secondary transfer roller 112 are in contact with each other via the conveyance path R. A fixing device 113 is provided on the downstream side of the secondary transfer portion in the conveyance path R. The fixing device 113 fixes the toner image transferred to the sheet S to the sheet S.

  2A is a perspective view of the scanning optical device (laser scanner) applied to the image forming apparatus of FIG. 1 with the lid member removed, and FIG. 2B is a plan view of the scanning optical device with the lid member removed. is there. 2C is a cross-sectional view taken along the line A-A ′ in FIG. 2B, and FIG. 2D is a perspective view showing a main configuration of the scanning optical device in FIG. 2A.

  2A to 2D, the laser scanner 104 includes an optical box 401 as a housing and a light source unit 200 attached to the optical box 104. The light source unit 200 includes a vertical cavity surface emitting laser (Vertical Cavity Surface Emitting Laser) 202 as a light source device and a laser driver 203 for driving the vertical cavity surface emitting laser (see FIG. 3 described later). A rotating polygon mirror that deflects laser light (light beam) emitted from the light source device 202 of the light source unit 200 so as to scan a photosensitive drum (not shown) in a predetermined direction is provided in the housing, that is, in the optical box 401. The polygon mirror 402 is accommodated. The polygon mirror 402 is integrally provided with a polygon motor 403 that is a driving source of the polygon mirror 402. The polygon motor 403 drives the polygon mirror 402. A beam splitter 410 is disposed on the optical path between the light source device 202 and the polygon mirror 402.

  The first fθ lens 404, the reflection mirror 405, the reflection mirror 406, the second fθ lens 407, the reflection mirror 408, and the dust proof are on the optical path of the first light beam that is transmitted through the beam splitter 410 and deflected by the polygon mirror 402. Glass 409 is disposed. The first fθ lens 404 is provided closer to the polygon mirror 402 than the second fθ lens 407. The light beam reflected by the reflection mirror 408 passes through the dust-proof glass 409 and is irradiated on a photosensitive drum (not shown). On the other hand, a condensing lens 415 and a photodiode (PD) 411 as a photoelectric conversion element (light receiving unit) are disposed in the optical path of the second light beam reflected by the beam splitter 410.

  In the optical box 401, a beam detector (hereinafter referred to as “BD sensor”) 412 and a BD sensor 412 that generate a synchronization signal for determining the light beam emission timing based on the image data are attached. A BD lens 413 is provided. Further, a thermistor 450 serving as a temperature detecting means is disposed on the drive circuit board of the polygon motor 403, more specifically, in a region surrounded by the wall surface of the optical box 401, the rib 416, and the fθ lens 404. The thermistor 450 detects the internal temperature of the optical box 401. The optical box 401 is sealed by attaching a lid 417 as a sealing member.

  In such a configuration, the light beam emitted from the light source device 202 of the light source unit 200 enters the beam splitter 410. The light beam incident on the beam splitter 410 is separated into a first light beam that is transmitted light and a second light beam that is reflected light. The first light beam is deflected by the polygon mirror 402, and passes through the first fθ lens 404, the reflection mirror 405, the projection mirror 406, the second fθ lens 407, the reflection mirror 408, and the dust-proof glass 409, and the photosensitive drum not shown. Irradiated at an equiangular velocity. That is, a light beam scanned at a constant angular velocity by the polygon mirror 402 scans on the photosensitive drum through the first fθ lens 404 and the second fθ lens 407 at a constant velocity, forms an image, and electrostatically forms on the surface of the photosensitive drum. A latent image is formed. At this time, a part of the first light beam passes through the first fθ lens 404, is reflected by the reflection mirror 405 and the BD mirror 414 (see FIG. 2D), and is a BD lens which is an optical system including a plurality of lenses. It passes through 413 and enters the BD sensor 412. The BD sensor 412 functions as a detection unit, detects a scanning timing of the light beam based on the incident light beam, and outputs a BD signal indicating a reference timing for starting image formation.

  On the other hand, the second laser light passes through the condenser lens 415 and then enters the photodiode (PD) 411. The PD 411 outputs a detection signal corresponding to the amount of received light, and performs automatic light amount control (Automatic Power Control: APC) based on the output detection signal.

  FIG. 3 is a block diagram showing a control system of the image forming apparatus including the scanning optical device 104 of FIGS. 2A to 2D.

  In FIG. 3, a CPU 501 as a control device is communicably connected to the image forming units 101Y, 101M, 101C, and 101B, the secondary transfer roller 112, the fixing device 113, and the memory 502. Since the elements of the control system in each image forming unit are the same, here, the control system of the image forming unit 101Y will be described as an example.

  The CPU 501 includes a clock signal generation unit such as a crystal oscillator that generates a clock signal having a frequency higher than that of the synchronization signal, and a counter that counts the clock signal. The CPU 501 is communicably connected to the BD sensor 412, the PD 411, the thermistor 450, and the process unit of the image forming unit 101Y. In addition, the CPU 501 is connected to the light source device 202 of the optical unit 200 through the laser driver 203 in communication capability.

  The CPU 501 controls each element based on a control program stored in the memory 502. The CPU 501 controls the secondary transfer roller 112 and the fixing device 113. The CPU 501 receives a synchronization signal output from the BD sensor 412, a detection signal output from the PD 411, and a detection signal output from the thermistor 450. The CPU 501 transmits a control signal to the laser driver 203 based on the synchronization signal, and the laser driver 203 transmits a drive signal to the light source device 202 based on the control signal. At that time, the CPU 501 predicts color misregistration based on the detection signal from the thermistor 450 and corrects the color misregistration by correcting the drive signal.

  The process unit includes a driving unit that drives the photosensitive drum 102Y, a charging device 103Y, a developing device 105Y, a drum cleaning device 106Y, a driving roller 108, and a primary transfer device 111Y. In addition to the control program, the memory 502 stores timing data that defines the emission timing of each light emitting element and color misregistration correction data.

  Next, an image forming process using the image forming apparatus 100 of FIG. 1 provided with the laser scanner 104 of FIGS. 2A to 2D will be described. Since the image forming process in each of the image forming units 101Y to 101Bk is the same, the following description focuses on the image forming process in the image forming unit 101Y.

  First, the charging device 103Y in the image forming unit 101Y uniformly charges the surface of the photosensitive member that is rotationally driven, that is, the surface of the photosensitive drum 102Y. Next, the laser scanner 104Y emits a light beam based on the image signal, scans and exposes the surface of the charged photosensitive drum 102Y, and forms an electrostatic latent image. Next, the developing device 105Y supplies toner to the electrostatic latent image formed on the surface of the photosensitive drum 102Y for visualization, thereby forming a yellow toner image. Similarly, toner images of corresponding colors are formed in the image forming units 101M, 101C, and 101Bk. The toner images formed on the respective photosensitive drums 102Y to 102Bk are transferred to the intermediate transfer belt 107 when the primary transfer devices 111Y to 111Bk apply a transfer bias to the intermediate transfer belt 107, and are superimposed to form a color image. .

  The color image formed on the intermediate transfer belt 107 is conveyed to a secondary transfer portion which is a nip portion between the driven roller 110 and the secondary transfer roller 112, and is here conveyed from the manual feed cassette 114 or the paper feed cassette 115. The image is transferred to the sheet S conveyed via the path R. The sheet S to which the color image has been transferred is conveyed to the fixing device 113 where the color image is heated and fixed to the sheet S. The sheet S on which the color image is fixed is discharged onto a paper discharge unit 117 by a paper discharge roller 116. The residual toner remaining on the photosensitive drums 102Y to 102Bk after the toner image is transferred to the intermediate transfer belt 107 is removed by the corresponding drum cleaning devices 106Y to 106Bk, and the same image forming process is executed thereafter.

  Next, an image forming process performed by the image forming apparatus 100 including the scanning optical device (laser scanner) 104 shown in FIGS. 2A to 2D will be described.

  FIG. 4 is a flowchart illustrating a procedure of image forming processing by the image forming apparatus including the scanning optical device (laser scanner) of FIGS. 2A to 2D. This image forming process is executed by a CPU 501 as a control device in accordance with an image forming process procedure of an image forming process program stored in the memory 502.

  In FIG. 4, when the image forming process is started, the CPU 501 first determines whether or not it is immediately after the power is turned on to the image forming apparatus 100 (step S100). If the result of determination in step S100 is that the power has just been turned on (“YES” in step S100), the CPU 501 executes warm-up processing (step S101), and prepares for forming a good image. The warm-up process includes various correction processes such as a color misregistration correction process, and corrects misalignment of the light beam irradiation position among multiple image forming units as the warm-up process is executed (registration). An initial state without color misregistration is formed. At this time, the temperature of the fixing device 113 is adjusted. It is assumed that the power is also turned on to the laser scanner 104 applied to the image forming apparatus 100 at the same time as the power is turned on to the image forming apparatus 100.

  After the series of warm-up processes (step S101) is completed, the CPU 501 stops the polygon motor 403 and stops the rotation of the polygon mirror 402 (step S109). At this time, as the polygon mirror 402 stops, the internal airflow of the laser scanner 104 stops, and the temperature detected by the thermistor 450, that is, the internal temperature of the laser scanner 104 rises.

  FIG. 5 is a diagram showing a change in the internal temperature of the laser scanner accompanying the start of rotation of the polygon mirror. The horizontal axis indicates the elapsed time, and the vertical axis indicates the internal temperature of the laser scanner 104, which is the detected temperature of the thermistor 450.

  In FIG. 5, during the warm-up process (step S101), the polygon mirror 402 is repeatedly started and stopped, and the detected temperature (internal temperature) of the thermistor 450 is lowered immediately after the polygon mirror 402 starts rotating. I understand that. The decrease in the internal temperature is due to the fact that when the polygon mirror 402 starts to rotate, an air flow 451 is generated in the optical box 401 as shown in FIG. 2C, and the air flow 451 collides with the thermistor 450 and takes heat away. doing.

  Returning to FIG. 4, after the rotation of the polygon mirror 402 is stopped (step S109), the CPU 501 determines whether or not the internal temperature is stabilized (step S110). As a result of the determination in step S110, if the internal temperature is stable (“YES” in step S110), the CPU 501 acquires and stores the internal temperature when it is stable (step S111). The temperature acquired in step S111 corresponds to T0 in FIG. 5 and serves as a reference temperature. Whether or not the temperature has stabilized in step S110 is determined as follows. That is, it is considered stable when the temperature change amount of the internal temperature per unit time is equal to or less than a predetermined threshold value. Further, a predetermined time until the temperature change amount of the internal temperature per unit time becomes equal to or less than a predetermined threshold is measured in advance in the design stage, and after the polygon mirror 402 is stopped (step S109), the predetermined time is set. When the time has passed, the internal temperature may be considered stable.

  Next, the CPU 501 determines whether or not the power supply has been stopped by the user (step 112), and terminates the process on the condition that the power supply has been stopped ("YES" in step S112). On the other hand, when the power is not stopped by the user and the power-on state is maintained (“NO” in step S112), the CPU 501 determines whether or not the process is immediately after turning on the power immediately after the start of the process ( It returns to step S102 which is the next step of step S100).

  Next, as a result of the determination in step S100, if it is not immediately after power-on (“NO” in step S100), the CPU 501 shifts the processing to the standby state (step S102). The standby state is a standby state for waiting for an input of a print job in which the rotation of the polygon mirror 402 is stopped. Next, after confirming that a print job has been input (step S103), the CPU 501 acquires the internal temperature detected by the thermistor 450 and stores it as the current internal temperature before the polygon mirror 402 starts rotating (step S103). S104). This current internal temperature corresponds to T (NOW) in FIG. In FIG. 5, the polygon motor 403 is stopped in the section of step S102, but the internal temperature is, for example, 0.5 (deg) due to the heat generated by the driver of the polygon motor 403 and the influence of other units such as the fixing device 113. ) It rises and is in a state where color misregistration occurs.

  After acquiring the current internal temperature (step S104), the CPU 501 starts rotating the polygon motor 403 and rotates the polygon mirror 402 (step S105). At this time, as shown in FIG. 5, the internal temperature apparently decreases with the generation of the air flow accompanying the rotation of the polygon mirror 402, but the temperature of the optical member hardly decreases. Therefore, in the present embodiment, in order to avoid such ambiguous control by applying the apparently lowered internal temperature, the following processing is performed.

  That is, before starting the image forming process (step S107), the CPU 501 executes a color misregistration prediction correction control process based on the difference between the current internal temperature stored in step S104 and the reference temperature acquired in step S111. (Step S106). Accordingly, it is possible to perform color misregistration prediction correction control based on the stable optical member temperature in the stopped state, not the apparent internal temperature that has become unstable with the start of rotation of the polygon mirror 402. The color shift prediction correction control process will be described later.

  The CPU 501 that has executed the color misregistration predictive correction control process then executes the image forming process (step S107), and continues the image forming process until the print job is completed (step S108). Next, after the print job is completed (“YES” in step S108), the CPU 501 stops the polygon motor 403 and stops the rotation of the polygon mirror 402 (step S109). After stopping the rotation of the polygon mirror 402, the CPU 501 shifts the process to step S110 to determine whether or not the internal temperature has stabilized, and then executes the same sequence as that after the end of the warm-up process.

  As a result of the determination in step S110, if the internal temperature is not stable (“NO” in step S110), the CPU 501 does not execute predictive correction control for color misregistration correction even if a print job is input. That is, when a print job is input before the internal temperature is stabilized (“YES” in step S113), the CPU 501 rotates the polygon mirror 402 (step S114), and performs image misregistration prediction correction control. A formation process is executed (step S107). If no job is input before the temperature stabilizes (“NO” in step S113), the CPU 501 waits until the internal temperature stabilizes (step S110).

  According to the process of FIG. 4, the image forming apparatus 100 is turned on, the warm-up process is executed, the rotation of the polygon mirror 402 is stopped, and then a print job is input before the internal temperature is stabilized. In this case, the color misregistration correction predictive control is not executed. As a result, it is possible to prevent execution of uncertain prediction correction control based on the fluctuating internal temperature.

  Next, the color misregistration prediction correction control process in step S106 of FIG. 4 will be described in detail.

  As the polygon mirror 402 starts rotating in step S105 of FIG. 4, the internal temperature rapidly decreases (see FIG. 5). However, the decrease in the internal temperature is caused by the generation of an air flow accompanying the rotation of the polygon mirror 402, and the actual temperature of optical members such as lenses and mirrors is not affected by the air flow and does not fluctuate. Will not cause. Therefore, if color misregistration predictive correction control is executed based on the detected temperature of the thermistor 450 immediately after the rotation of the polygon mirror 402 is started, erroneous control will occur. For this reason, in the present embodiment, in the first predictive correction control after a print job is input, not based on the internal temperature after the rotation of the polygon mirror 402 starts but based on the internal temperature in the stop state before the rotation starts. Predictive correction control is executed. This prevents erroneous control in predictive correction control.

  FIG. 6 is a flowchart showing the procedure of the color misregistration prediction correction control process in step 106 of FIG.

  In FIG. 6, when the color misregistration prediction correction control process is started, the CPU 501 first acquires the internal temperature (T (NOW)) before the rotation of the polygon mirror 402 acquired in step S104 and the reference acquired in step S111. The temperature is compared (step S201). Next, the CPU 501 calls a correction coefficient stored in the memory 502, and calculates a color shift change amount predicted based on the correction coefficient and a temperature difference between the internal temperature (T (NOW)) and the reference temperature (step). S202).

  FIG. 7 is a diagram showing the relationship between the temperature rise amount of the internal temperature and the color shift change amount in the laser scanner (scanning optical device) of FIG.

  In FIG. 7, the slope of the straight line is the correction coefficient. The correction coefficient is obtained by performing a continuous printing operation or a printing operation after being left in a standby state at the design stage, and measuring a color misregistration amount and a detection temperature on the image. The same measurement can be performed for a plurality of aircraft, and the data can be averaged to obtain a product-specific coefficient.

Here, the predicted value Δ of the color shift change amount is expressed as follows.
Δ = (T (NOW) −T0) × 28.4 (Equation 1)

  Here, T (NOW) is a current internal temperature, T0 is a reference temperature, and 28.4 is a correction coefficient.

  Since the image forming apparatus in FIG. 1 is, for example, 2400 dpi, one line corresponds to 10.8 μm. For example, if the temperature rise amount is 0.5 d (deg) and the color shift change amount in the sub-scanning direction is 14.2 μm, the exposure timing for one line is corrected. In this embodiment, since a multi-beam laser scanner is used, the irradiation timing to the drum is corrected by shifting the beam to be exposed by one line compared to before correction.

  Returning to FIG. 6, after calculating the color shift change amount, the CPU 501 corrects the signal timing of the synchronization signal and the drive signal of the light emitting device 202 according to the calculated color shift change amount (step S <b> 203). Correction control is executed, and this process is terminated.

  According to the process of FIG. 6, when the internal temperature temporarily fluctuates, that is, decreases with the start of rotation of the polygon mirror 402, in the first correction control, the internal temperature and the reference temperature before the rotation of the polygon mirror 402 is started. Predictive correction control is executed based on the temperature difference between Thereby, it is possible to improve the accuracy of the correction control process by suppressing the erroneous correction control based on the apparent decrease in the internal temperature caused by the air flow generated when the polygon mirror 402 starts to rotate.

  Here, the control performed within one scanning cycle in which the laser beam is scanned once will be described.

  FIG. 8 is a diagram illustrating signal timings of the synchronization signal and the drive signal in the light emitting device 202 of the optical unit 200.

  In FIG. 8, (1) shows an output signal from the BD sensor 412, and (2) shows a drive signal transmitted from the laser driver 203 to the light emitting element A among the plurality of light emitting elements of the light emitting device 202. . Further, (3) shows a drive signal transmitted from the laser driver 203 to the light emitting element B among the plurality of light emitting elements of the light emitting device 202. For the sake of simplicity, only the light emitting elements A and B are shown, but the number of light emitting elements may be three or more.

  As shown in (2) of FIG. 8, the laser driver 203 transmits a drive signal to the light emitting element A in accordance with the timing of entering the BD sensor 412 in order to generate a synchronization signal. Laser light is emitted from the light emitting element A according to the drive signal, and the BD 412 that receives the laser light generates a BD signal.

  The CPU 501 determines an exposure start position (image formation start position) in the main scanning direction based on the generation timing of the synchronization signal. The CPU 501 captures an image in response to the count value counted in response to the generation of the synchronization signal being a first predetermined value (one of the timing data) set for each light emitting element. The laser driver 203 is started to emit laser light based on the data. That is, as shown in (2) and (3) of FIG. 4, the CPU 501 forms a toner image on the photosensitive drum after a predetermined time T21 and T22 corresponding to the first predetermined value after the generation of the synchronization signal. The laser driver 203 starts emitting laser light for this purpose. Thereafter, laser light based on the image data is emitted from the light emitting elements A and B in the latent image formation periods of (2) and (3) in FIG.

  Further, the CPU 501 resets the count value of the counter and starts counting in response to the generation of the synchronization signal. Then, the CPU 501 sets each light emitting element of the optical device 202 in response to the count value of the counter reaching a second predetermined value (one of the timing data) set corresponding to each light emitting element. Light up individually. In addition, the CPU 501 executes APC for each light emitting element based on the light reception result of receiving the laser light emitted from each light emitting element. That is, as shown in FIG. 8, the CPU 501 executes APC after predetermined times T11 and T12 corresponding to the second predetermined value after the synchronization signal is generated. APC is executed during the APC execution period shown in FIG.

  Note that the first predetermined value and the second predetermined value set for each light emitting element are BD412 and PD411 when the laser light scanned on the rotary polygon mirror is taken into account in consideration of the rotation speed of the rotary polygon mirror. Is set based on the timing at which the light enters. In the present embodiment, the first predetermined value and the second predetermined value have been described as the predetermined values set corresponding to the respective light emitting elements. However, the first predetermined value and the second predetermined value are It may be a predetermined value set in common to the light emitting elements.

  Further, the CPU 501 compares the voltage of the detection signal output from the PD 411 with a reference voltage corresponding to the target light amount (corresponding to reference data stored in the memory 502), and supplies it to each light emitting element based on the voltage difference. A drive current value which is a drive signal to be controlled is controlled. That is, when the voltage of the detection signal output from the PD 411 is lower than the voltage corresponding to the target light amount, the drive current supplied to the light emitting element is increased to increase the light amount of the laser light. On the other hand, when the voltage of the detection signal output from the PD 411 is higher than the voltage corresponding to the target light amount, the current supplied from the laser driver 203 to the light emitting element is decreased to reduce the light amount of the laser light.

  According to the process of FIG. 6, the first predictive correction control after the print job is input is executed based on the internal temperature before the rotation start, not after the polygon mirror rotation start. Thus, it is possible to prevent erroneous control in the prediction correction control and perform accurate prediction correction control.

  In the present embodiment, the thermistor 450 is preferably disposed on the drive circuit board of the polygun motor 403 that drives the polygon mirror 402. The thermistor 450 is disposed in a region surrounded by the wall surface of the optical box 401 around the polygon mirror 402 and the imaging lens (fθ lens 404) disposed closest to the polygon mirror 402. More preferably. Since this region has the largest temperature change (temperature increase) amount in the laser scanner 104, the sensitivity in control can be reduced and the S / N can be kept good.

  In this embodiment, the color image forming apparatus and the laser scanner applied thereto are described as examples. However, the image forming apparatus and the like are not limited to these. That is, the image forming apparatus or the like may be an image forming apparatus that forms an image with a single color toner, for example, black, and a laser scanner applied thereto.

  In the present embodiment, the case where the exposure timing in the sub-scanning direction is corrected in order to perform color misregistration correction has been described, but the correction control target is not limited to this. That is, for example, control for performing correction in the main scanning direction in order to execute color misregistration correction may be performed. The main scanning direction can be corrected by changing the time from the synchronization signal until the exposure is performed in the control performed within one scanning cycle in which the light beam shown in FIG. 8 is scanned once.

  In a multi-beam type laser scanner, the beam interval in the main scanning direction changes with the temperature rise of the lens, and periodic density unevenness or moire may occur due to interference with the screen. In order to solve the problem, the present invention can be applied. In this case, it is possible to correct the exposure timing in the main scanning direction by obtaining correction coefficients for the temperature change and the main scanning interval at the time of design and executing correction control based on the correction coefficients.

  9A and 9B are diagrams for explaining a scanning optical apparatus equipped with a multi-beam type light source. FIG. 9A is a perspective view showing a main configuration, and FIG. FIG. 9C is a diagram showing the imaging position before the temperature rise, and FIG. 9C is a diagram showing the beam optical path and the imaging position after the temperature rise.

  In FIG. 9A, the main configuration of the laser scanner 104 is the same as that of the laser scanner 104 shown in FIG.

  The light beam emitted from the light source device 202 having a plurality of light emitting units enters the polygon mirror 402 through the beam splitter 410 and is deflected by the polygon mirror 402. The light beam deflected by the polygon mirror 402 is scanned on a photosensitive drum (not shown) via the first fθ lens 404, the reflection mirror 405, the reflection mirror 406, the second fθ lens 407, and the reflection mirror 408. The surface of the photosensitive drum is exposed to form an electrostatic latent image.

  In FIGS. 9B and 9C showing a plurality of optical paths of the light beam that scans the surface of the photosensitive drum, assuming that there is no optical focus shift in the main scanning direction, the mth laser LDm and the nth laser beam are assumed. The lasers LDn follow different optical paths and reach the surface of the photosensitive drum. For this reason, laser scanners equipped with a multi-beam type light source generally measure the passage time difference of each beam in advance at the time of factory shipment, and control the emission timing of each beam based on the time difference. The dot positions of each beam are controlled to be aligned. The irradiation timing of each beam is measured at the time of factory shipment when the temperature of the constituent members is not increased. Accordingly, before the temperature of the laser scanner rises, dots are aligned at each image position on the surface of the photosensitive drum as shown in FIG. 9B by emitting light based on the issuance timing measured in advance. .

  On the other hand, when the internal temperature of the apparatus rises due to the rotation of the polygon motor or each heat source in the image forming apparatus, the focus position of the scanning optical apparatus changes due to the thermal expansion of each member or the change in the refractive index of the optical components. To do. The light emission timing measured in advance in the factory is measured in a state where there is no focus deviation before the temperature rise. After the light emission occurs according to this issuance timing, after the focus deviation occurs, as shown in FIG. In addition, the dots are aligned when the focus is shifted. It is desirable that the relative dot positions in each beam are aligned in the vertical direction on the drum surface, that is, not shifted in the main scanning direction. However, if a focus shift occurs due to a rise in temperature, the main scanning is performed on the photosensitive drum surface. A relative dot position shift between the beams occurs in the direction. Since the dot position shift causes a periodic change in the exposure position, it easily causes interference with the screen to be used and causes image moire.

  FIG. 10 is a diagram showing the correlation between the amount of change in the internal temperature of the laser scanner 104 and the amount of change in the relative dot position in the main scanning direction between the beams. In FIG. 10, the amount of change (μm) in the position information in the main scanning direction of the dot that is the measurement image has a linear correlation with the amount of change (deg) in the internal temperature. Therefore, as in the case of color misregistration correction, it can be seen that predictive control can be performed based on a change in internal temperature using a thermistor.

  However, immediately after the polygon mirror 402 shifts to the rotation state, the internal temperature temporarily decreases based on the generation of the air flow. Therefore, when the color misregistration correction is executed based on the detected temperature immediately after the polygon mirror 402 starts rotating, the control is performed. An error occurs. Therefore, in the present embodiment, in order to prevent a control error based on a detection temperature that is a detection result immediately after the rotation of the polygon mirror 402 is started, when the internal temperature temporarily decreases immediately after the rotation starts, the polygon mirror 402 Predictive correction control is performed based on the measurement result before the start of rotation. As a result, it is possible to restrict the predictive control based on the apparently changed internal temperature and prevent the occurrence of a control error. The dot position deviation correction restriction process is executed according to the same sequence as the color deviation correction restriction process in FIG.

  In this embodiment, the thermistor 450 mounted on the drive circuit board of the polygon motor is applied as the internal temperature detection sensor. However, the present invention is not limited to this. For example, around the polygon motor or the fθ lens. An affixed thermocouple can also be applied. In the present embodiment, the arrangement of the optical members in the laser scanner is not particularly limited. If the rotating member such as the polygon mirror 402 is applied, the optical arrangement of each member is as follows. Any configuration may be used.

  In the present embodiment, the control subject to restriction is not limited to color misregistration correction or dot position misalignment correction between beams, but is changed by increasing the temperature and corrected by changing the exposure timing of the laser scanner. Any characteristic value may be controlled as long as it is a characteristic value. Further, the correlation between the characteristic value of the controlled object and the temperature does not need to be linear as described above, and one correction amount is provided for the temperature rise amount even if the correlation is a curve or other correlation. Any correlation may be used as long as it is determined as follows.

100 image forming apparatuses 101Y to 101Bk image forming units 102Y to 102Bk photosensitive drums 103Y to 103Bk charging devices 104Y to 104Bk scanning optical devices (laser scanners)
105Y to 105Bk Developing devices 106Y to 106Bk Drum cleaning device 107 Intermediate transfer belt 108 Driving roller 401 Optical box 402 Polygon mirror (rotating polygon mirror)
404, 407 fθ lens 412 BD sensor 414 BD mirror 416 wall surface 450 thermistor 501 CPU

Claims (6)

A photoreceptor,
A rotary polygon mirror that deflects light emitted from the light source; a drive unit that rotates the rotary polygon mirror; and a housing that houses the light source and the rotary polygon mirror. An exposure device that exposes the photoconductor with light deflected by a mirror to form an electrostatic latent image on the photoconductor;
A developing device for developing the electrostatic latent image on the photoreceptor to form an image;
A temperature detecting means provided inside the housing for detecting the temperature of the exposure apparatus ;
At a second timing before the rotation polygon mirror starts to rotate after the first timing, the temperature detection means detects the first temperature at a first timing with the rotation polygon mirror stopped rotating. Determining means for causing the temperature detecting means to detect a second temperature and determining a color misregistration amount based on the first temperature and the second temperature ;
Correction means for correcting the exposure timing after the rotary polygon mirror starts rotating so that the exposure apparatus exposes the photoconductor based on image data based on the color misregistration amount determined by the determination means. image forming apparatus characterized by having, when. The image forming apparatus further includes a control unit that executes a warm-up process ,
The control means executes the warm-up process after the image forming apparatus is powered on;
The said determination means makes the said temperature detection means detect the said 1st temperature in the 1st timing in the state which the said rotation polygon mirror stopped rotating after the said warm-up process was performed. the image forming apparatus according to 1. It said determining means, when the change amount per predetermined time of the temperature detected by said temperature detecting means is equal to or less than the threshold value, characterized in that to detect the first temperature to the temperature sensing means The image forming apparatus according to claim 1 . The determination unit updates the first temperature based on a detection result of the temperature detection unit after the image formation based on the image data is completed and the rotary polygon mirror stops rotating. The image forming apparatus according to claim 1. It said temperature sensing means, an image forming apparatus according to any one of claims 1 to 4, characterized in that provided in the driver circuit board of the rotary polygon mirror. It said temperature sensing means, an image forming apparatus according to any one of claims 1 to 4, characterized in that air flow generated by rotation of the rotary polygon mirror is provided at a position such as to lower the detected temperature.