JP5473550B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus that specifies which of a plurality of reflecting surfaces of a polygon mirror a laser beam enters and controls a light source according to the reflecting surface.

  An electrophotographic image forming apparatus deflects and scans laser light with a rotating polygon mirror having a plurality of reflecting surfaces, and an electrostatic latent image is formed on an image carrier such as a photosensitive member by the laser light subjected to the deflection scanning. Form. The electrostatic latent image is developed with toner, and the toner image is transferred and fixed on the recording medium to form an image on the recording medium.

  The manufacturing accuracy of the polygon mirror is limited, and the reflectance of light on each reflecting surface of the polygon mirror is different. In addition, the amount of tilt (surface tilt) of each reflecting surface with respect to the rotation axis of the polygon mirror is different. For this reason, in an electrophotographic image forming apparatus, the image quality deteriorates due to a difference in reflectance and a surface tilt amount for each reflecting surface. That is, the amount of laser light after reflection is not uniform due to the difference in reflectivity for each reflection surface. In addition, the optical path after reflection of the laser light incident on a certain reflective surface differs from the optical path after reflection of the laser light incident on another reflective surface due to the difference in surface tilt amount for each reflective surface. As a result, the imaging position of the laser beam reflected by each of the reflecting surfaces of the polygon mirror on the photosensitive member is not constant, and the scanning lines when the photosensitive member is scanned are sparse and dense. As a result, the image density becomes non-uniform and the image quality deteriorates.

  A method of identifying which surface of a polygon mirror that is rotating during image formation is incident and correcting the light amount of the laser light in accordance with each reflecting surface against such a decrease in image quality Has been proposed (for example, Patent Document 1). The image forming apparatus described in Patent Literature 1 specifies a reflection surface on which laser light is incident by using a BD signal generated by detecting laser light reflected by adjacent reflection surfaces. The BD signal (Beam Detect signal) is a signal generated to synchronize the image writing position in the rotation axis direction of the photosensitive member. A Beam Detector (hereinafter referred to as BD) is disposed on a scanning line scanned with laser light. A BD signal is generated based on the light reception data of the BD that has received the laser light. Laser light is emitted after a lapse of a predetermined time from the generation of the BD signal, and formation of an electrostatic latent image is started. This makes it possible to align the writing start position in the direction in which the laser beam is scanned (main scanning direction). In Patent Document 1, the reflection surface on which the laser light is incident is specified by utilizing the fact that the period of the BD signal corresponding to each reflection surface is different for each reflection surface. That is, the difference between the period of the BD signal generated by the laser light reflected by the first surface and the second surface and the period of the BD signal generated by the laser light reflected by the second surface and the third surface, respectively. Is used to identify the reflecting surface on which the laser light is incident. Then, based on the specified result, correction data corresponding to each reflecting surface is read from the memory.

JP 2007-062223 A

  However, since the reference value stored in the memory is information at the time of shipment from the factory, if dirt is attached to the reflecting surface of the polygon mirror, the reflectance of the reflecting surface is lowered. The BD signal is generated based on the comparison result by comparing the light reception data output from the BD with a threshold value. When the reflectivity decreases, the amount of laser light incident on the BD decreases. Therefore, when the BD signal is generated, the rise and fall timings of the BD signal change, and the comparison result between the received light data and the threshold is the reflectivity. It changes greatly compared with before it falls. Thereby, the period of the detected BD signal changes. For this reason, the BD cycle for each reflecting surface of the polygon mirror is greatly different from that at the time of shipment from the factory, and there is a possibility that incorrect data is read from the memory and corrected.

The present invention has been made in view of the above problems, and an image forming apparatus according to the present invention includes a photoconductor, a light source that emits a light beam to form an electrostatic latent image on the photoconductor, and a plurality of reflections. A rotating polygon mirror having a surface, and a driving means for rotating the rotating polygon mirror, and the light beam emitted from the light source is scanned by the rotating polygon mirror so that the light beam is scanned on the photosensitive member. A deflecting means for deflecting; a detecting means for outputting a detection signal in response to receiving a light beam deflected by the rotary polygon mirror; and a light beam from the light source in an amount corresponding to a reflecting surface on which the light beam is incident. And correction means for correcting the light quantity of the light beam so as to be emitted so as to correspond to each of a plurality of reference data, and reflection by an adjacent reflection surface among the plurality of reflection surfaces Correlation between periodic data, which is a time interval of a detection signal output from the detection means by receiving the received light beam, and the plurality of reference data is obtained, and the plurality of reflecting surfaces based on the correlation Each of the plurality of correction data is individually associated with each other, and correction data corresponding to a reflecting surface on which the light beam is incident when the electrostatic latent image is formed is read from the storage unit, and based on the correction data Control means for correcting the light quantity of the light beam, and light source driving means for emitting a light beam from the light source with the light quantity corrected by the control means based on image data , the control means, The reference data is stored in the storage means so that the periodic data output from the detection means based on the correlation corresponds to the plurality of reflection surfaces. Characterized in that the update.

  According to the image forming apparatus of the present invention, even when the reflecting surface of the rotary polygon mirror is dirty, correction data corresponding to the reflecting surface on which the light beam is incident can be read from the memory.

1 is a schematic diagram of an image forming apparatus. 1A is a schematic diagram showing a scanning optical device and a photosensitive drum, and FIG. 1 is a block diagram of an image forming apparatus according to Embodiment 1. FIG. It is the schematic of the polygon mirror explaining a plane fall. FIG. 5 is a schematic diagram of a photosensitive drum for explaining variations in scanning line intervals caused by surface tilt. 3 is a flowchart of control executed by a CPU in the first embodiment. 3 is a flowchart of control executed by a CPU in the first embodiment. 3 is a flowchart of control executed by a CPU in the first embodiment. FIG. 6 is a block diagram of an image forming apparatus according to a second embodiment. It is the schematic of an operation part. 10 is a flowchart of control executed by a CPU in Embodiment 2.

Example 1
FIG. 1 is a schematic cross-sectional view of the entire image forming apparatus according to the present embodiment. First, the image forming apparatus 100 and the image forming process will be described with reference to FIG. Documents placed on the document table 102 of the document reading apparatus 101 are sequentially conveyed onto the surface of the document table glass 103. The document irradiating lamp unit 105 of the reading unit 104 is turned on so that the document is conveyed, and the reading unit 104 irradiates light while moving in the direction of the arrow X in the drawing. Reflected light from the original passes through the lens 109 via the mirrors 106, 107, and 108 and then enters the image sensor unit 110. Reflected light from the document incident on the image sensor unit 110 is temporarily stored in an image memory (not shown), read out again from the image memory, and then input to a scanning optical device 111 described later. The scanning optical device 111 emits laser light from a scanning optical device described later based on the image signal. The light is guided to a photosensitive drum 113 (photoconductor) whose surface is uniformly charged by a primary charger 112 through a reflection mirror or the like. An electrostatic latent image having a potential different from the charged potential is formed in a portion exposed by the laser beam. This electrostatic latent image is developed as a toner image by the developing device 114. A recording medium such as paper is conveyed from the stacking unit 115 or 116 in synchronization with the formation timing of the electrostatic latent image. Then, the developed toner image is transferred to a recording medium by a transfer device 117 disposed in the transfer unit. The transferred toner image is fixed on the recording medium by the fixing device 118 and then discharged to the outside by the paper discharge roller 119. The toner remaining on the surface of the photoconductor 113 after the transfer is cleaned by the cleaner 120, the surface of the photoconductor 113 is neutralized by the auxiliary charger 121, and the primary charger 112 is charged well when the next image is formed. To get. Next, the residual charge on the photoconductor 113 is erased by the pre-exposure lamp 122. Image formation is performed by repeating the above image forming process.

  Next, the scanning optical device 111 of this embodiment will be described with reference to FIG. FIG. 2A is a schematic top view schematically showing the scanning optical device 111 provided in the image forming apparatus 100 according to the present embodiment and the photoconductor 113 provided in the image forming apparatus 100. A scanning optical device 111 serving as a deflection scanning unit includes a semiconductor laser 201, a collimator lens 202, a diaphragm 203, a polygon mirror 204 serving as a rotary polygon mirror, an optical element group 205 such as an f-θ lens, and a detection unit. However, a Beam Detector 206 (hereinafter referred to as BD 206) is provided. Each element provided in the scanning optical device is accommodated in a housing 207.

  Laser light emitted from the semiconductor laser 201 is converted into substantially parallel light by the collimator lens 202 and the diaphragm 203 and enters the polygon mirror 204 with a predetermined beam diameter. The polygon mirror 204 is rotated in the direction of arrow R in FIG. 2 by a polygon mirror driving unit (described later) serving as a rotation driving means. With this rotation, the light beam incident on the reflecting surface of the polygon mirror 204 scans on the photosensitive drum in the direction of arrow Y (the rotational axis direction of the photosensitive drum, the main scanning direction). The laser beam deflected and scanned by the polygon mirror 204 receives a condensing action from an optical element group 205 including an f-θ lens provided between the polygon mirror 204 and the photosensitive drum. The f-θ lens is provided to correct distortion so as to guarantee the temporal linearity of scanning, and the light beam that has passed through the f-θ lens is on the photosensitive member 113 in the direction of arrow Y. Scanned at a constant speed. The photosensitive drum 113 is rotationally driven by a drum driving unit described later. For this reason, scanning of the laser beam in the arrow Y direction is repeatedly performed in the arrow Z direction (rotation direction, sub-scanning direction) during image formation. In this way, an electrostatic latent image can be formed on the photosensitive drum 113 by performing scanning in the main scanning direction and the sub-scanning direction with laser light.

  The BD 206 is a sensor that receives reflected light from the polygon mirror 204 and generates a BD signal based on the light reception result. The BD 206 is provided on the upstream side (scanning start side) of the photosensitive drum in the main scanning direction. The BD 206 photoelectrically converts the result of receiving the laser beam and compares the photoelectrically converted data based on a predetermined value to generate a BD signal as a detection signal.

  Next, the semiconductor laser 201 will be described in more detail. The semiconductor laser 201 includes a plurality of light emission sources (light emission sources 201A, 201B, 201C, 201D). FIG. 2B schematically shows an arrangement of a plurality of light emitting sources. Each light source is controlled by individual image data. Laser light emitted from a plurality of light sources is reflected by the same reflecting surface of the polygon mirror 204. Accordingly, in the image forming apparatus according to the present exemplary embodiment, a plurality of laser beams emitted from the plurality of light emission sources 201A, 201B, 201C, and 201D simultaneously scan the photosensitive drum in the sub-scanning direction on the photosensitive member in one scan. can do. The laser beams emitted from the light emission sources 201A, 201B, 201C, and 201D scan different positions on the photosensitive drum in the direction of arrow Z in FIG. In this embodiment, a semiconductor laser is described as an example, but an LED that emits a light beam may be used as a light source.

  FIG. 3 is a block diagram of the image forming apparatus according to the present embodiment. The image forming apparatus according to the present exemplary embodiment includes a CPU 301 serving as a control unit, a BD 206, an image data input unit 302, an image processing unit 303, a memory 304 serving as a storage unit, and a laser driving unit 305 serving as a light source driving unit. A semiconductor laser 201 serving as a light source is provided. The image forming apparatus according to the present exemplary embodiment includes a polygon mirror driving unit 306, a polygon mirror driving motor 307, a drum driving unit 308, and a drum driving motor 309. The memory 304 stores a control flow executed by the CPU 301, and the CPU 301 stores an image data input unit 302, an image processing unit 303, a memory 304, a laser driving unit 305, and a polygon mirror driving unit 306 based on the control flow. The drum driving unit 308 is controlled. The image data input unit 302 receives image data from an external device such as a PC or a reading device. The CPU 301 outputs an acceleration signal to each of the polygon mirror driving unit 306 and the drum driving unit 308 in response to image data being input to the image data input unit 302. The polygon mirror drive unit 306 increases the rotation speed of the polygon mirror drive motor 307 accordingly, and the drum drive unit 308 increases the rotation speed of the drum drive motor 309. Further, the CPU 301 outputs a deceleration signal to the polygon mirror drive motor 307 when it is necessary to decelerate the rotation speed of the polygon mirror 204. The polygon mirror driving unit 306 decreases the rotation speed of the polygon mirror driving motor 307 accordingly. Further, the CPU 301 outputs a deceleration signal to the drum driving unit 308 when it is necessary to decelerate the rotation speed of the photosensitive drum 113. The drum driving unit 308 decreases the number of rotations of the drum driving motor 309 accordingly. The CPU 301 transmits an instruction for emitting laser light from the semiconductor laser to the laser driving unit 305 in response to the rotation speeds of the polygon mirror 204 and the photosensitive drum 113 being stabilized.

  The CPU 301 outputs a drive signal to the laser drive unit 305 so that the semiconductor laser 201 emits laser light after a predetermined time after detecting the BD signal. Thus, by controlling the emission timing of the laser beam based on the BD signal, the image writing position in the main scanning direction for each scan is made uniform. Further, the CPU 301 compares the cycle of the BD signal with predetermined cycle data, and controls the rotation speed of the polygon mirror based on the comparison result. When the period of the BD signal is longer than the predetermined period, the CPU 301 outputs an acceleration signal to the polygon mirror driving unit 306. On the other hand, when the period of the BD signal is shorter than the predetermined period, the CPU 301 outputs a deceleration signal to the polygon mirror driving unit 306. The example in which the rotation speed of the polygon mirror is controlled based on the BD cycle of the BD signal output from the BD 206 has been described. However, in consideration of control responsiveness, a divided signal is usually generated by dividing the generated BD signal, the divided signal is compared with a predetermined period, and the rotation speed of the polygon mirror is based on the comparison result. Acceleration / deceleration control is performed.

  The image data input to the image data input unit 302 is transmitted to the image processing unit 303 in accordance with an instruction from the CPU 301, and predetermined processing is performed in the image processing unit 303. The corrected image data is transmitted to the laser driving unit 305. On the other hand, the laser driving unit 305 uses laser light emitted from the light emission sources 201A, 201B, 201C, and 201D of the semiconductor laser 201 using correction data (details will be described later) stored in the memory in response to an instruction from the CPU 301. Correct the amount of light. For example, the laser driving unit 305 receives an instruction to adjust the pulse width of the pulse signal for driving the semiconductor laser 201 from the CPU 301 and adjusts the pulse width based on the correction data. The laser driver 305 emits laser light from the semiconductor laser based on the adjusted pulse signal and the image data processed by the image processor 303. The laser driving unit 305 adjusts the driving current supplied to the semiconductor laser 201 from a power source (not shown) in response to receiving an instruction to adjust the light amount of the light beam emitted from the semiconductor laser 201 from the CPU 301, The amount of light may be adjusted. The laser drive unit 305 emits laser light from the semiconductor laser 201 based on the adjusted light amount and the image data processed by the image processing unit 303.

  Here, a method for changing the light amounts of the light emitting sources 201A, 201B, 201C, and 201D of the semiconductor laser 201 for each of the plurality of reflecting surfaces of the polygon mirror 204 will be described. As described above, the plurality of reflecting surfaces of the polygon mirror 204 have different reflectances. Therefore, the light amount of the laser light is corrected for each reflection surface on which the laser light is incident so that the light amount after reflection is uniform.

  Further, the plurality of reflecting surfaces of the polygon mirror 204 have different tilt amounts (surface tilt amounts) with respect to the rotation shaft 204a. FIG. 4 is a diagram for explaining the plane collapse. The polygon mirror 204 rotates around the rotation axis 204A. The arrows in FIGS. 4A and 4B indicate the optical paths of the laser light incident on the reflecting surface and the reflected laser light. In this embodiment, in order to simplify the description, the ideal optical path is an optical path in which the optical path of the incident laser light and the reflected laser light overlap.

  As shown in FIG. 4, the reflective surface M (FIG. 4A) and the reflective surface N (FIG. 4B) are inclined with respect to the rotating shaft 204 </ b> A, and the amount of tilt with respect to the rotating shaft is different. Therefore, the optical path after reflection differs between the two reflecting surfaces. As a result, as shown in FIG. 5, there is a variation (dense / dense) in the interval between the scanning lines formed on the photosensitive drum. FIG. 5A shows scanning lines formed on the photoconductor when the reflecting surface N is provided next to the reflecting surface M and the reflecting surface N is provided on the downstream side of the reflecting surface M in the rotation direction. It is the figure represented typically. Lines 1 to 4 in FIG. 5 (a) are scanning lines formed by a single scan in which the laser light emitted from the light emitting sources 201A, 201B, 201C, and 201D is reflected by the reflecting surface M. Lines 5 to 8 are scanning lines that are reflected by the reflecting surface N and formed by a single scan. The interval between adjacent scanning lines from line 1 to line 4 and the interval between adjacent scanning lines from line 5 to line 8 are the arrangement intervals of the plurality of light emitting sources 201A, 201B, 201C, 201D shown in FIG. It is constant because it depends. On the other hand, the distance between the line 4 and the line 5 is affected by the surface tilt, so that the distance between the scanning lines is narrowed. Since the distance between the line 4 and the line 5 is narrow, the density of this portion is high.

  On the other hand, FIG. 5B shows a scan formed on the photosensitive drum when the reflecting surface N is provided next to the reflecting surface M and the reflecting surface M is provided on the downstream side of the reflecting surface N in the rotation direction. It is the figure which represented the line typically. The interval between adjacent scanning lines from line 1 to line 4 and the interval between adjacent scanning lines from line 5 to line 8 are constant because they depend on the arrangement interval of the plurality of light emitting sources shown in FIG. However, since the interval between the line 4 and the line 5 is affected by the surface tilt, the interval between the scanning lines is widened. Since the distance between the line 4 and the line 5 is wide, the density of this portion is low.

  In this way, the image density is uneven due to the influence of the surface tilt. Such uneven image density can be corrected by adjusting the amount of laser light. For example, when a portion where the scanning line interval is narrowed as shown in FIG. 5A occurs, at least one light amount of the laser light forming the line 4 and the line 5 constituting the portion where the scanning line interval is narrowed is reduced. Let That is, when the laser beam reflected by the reflecting surface M is emitted, the light amount of the light source 201D (see FIG. 2B) that scans the line 4 is reduced, or the laser beam reflected by the reflecting surface N is emitted. In this case, the light amount of the light source 201A (see FIG. 2B) that scans the line 5 is reduced. You may control to reduce the light quantity of both light source 201D and light source 201A.

  On the other hand, as shown in FIG. 5A, when a portion having a wide scanning line interval is generated, the amount of laser light forming at least one of the line 4 and the line 5 constituting the portion having the wide scanning line interval is increased. . That is, the light amount of the light source 201D that scans the line 4 when the laser beam reflected by the reflecting surface M is emitted is increased, or the light source that scans the line 5 when the laser beam reflected by the reflecting surface N is emitted. The amount of light of 201A is increased. In this way, by controlling the amount of laser light that differs for each reflecting surface, the uneven density becomes inconspicuous visually. In the correction of the light amount, the CPU 301 reads the correction data stored in the memory 304 from the memory, and corrects the input image data with the correction data.

  The memory 304 stores correction data for correcting the amount of laser light emitted from each of the light emission sources 201A, 201B, 201C, and 201D of the semiconductor laser 201. This correction data is data for correcting the difference in reflectance for each reflecting surface. For example, when it is known at the time of shipment from the factory that the reflectance of the second surface is lower than that of the first surface of the polygon mirror, the difference in the amount of light after reflection is performed in order to suppress the occurrence of density unevenness due to the difference in reflectance. Need to be corrected. Therefore, the semiconductor laser is controlled so that the amount of laser light incident on the second surface is higher than the amount of laser light incident on the first surface. Alternatively, the semiconductor laser is controlled so that the amount of laser light incident on the second surface is lower than the amount of laser light incident on the first surface. The memory 304 stores correction data for performing this light amount correction. Note that the correction data stored in the memory 304 may be data for correcting density unevenness generated in the image due to the influence of surface tilt by correcting the light amount.

  The correction data is correction data specific to each reflecting surface of the polygon mirror 204. That is, as shown in Table 1, in the memory 304, correction data a for correcting the amount of laser light incident on the A surface of the polygon mirror 204, correction data b for correcting the amount of laser light incident on the B surface, Correction data c for correcting the amount of laser light incident on the C surface, correction data d for correcting the amount of laser light incident on the D surface, and correction data e for correcting the amount of laser light incident on the E surface are stored. ing. When emitting the laser light incident on the A-th surface, the CPU 301 reads the correction data a from the memory 304 and corrects the light amount of the laser light emitted from the light emission sources 201A, 201B, 201C, and 201D with the correction data a. The laser driving unit 305 emits a laser beam having a light amount corrected based on the image data corrected by the image processing unit 303.

  In order to correct the amount of laser light emitted from the semiconductor laser 201 in accordance with the reflecting surface that reflects the laser light, the laser light is applied to any of the reflecting surfaces while the polygon mirror 204 is rotated. It is necessary to specify whether it is incident. In the following, a method for specifying which of the plurality of reflecting surfaces of the polygon mirror the laser beam enters by using the periodic data of the BD signal will be described.

  A polygon mirror 204 having five reflecting surfaces of A surface, B surface, C surface, D surface, and E surface will be described as an example. When the polygon mirror 204 is rotating, the laser light sequentially enters the A, B, C, D, and E surfaces, which are the reflecting surfaces of the polygon mirror 204, and then enters the A surface again after the E surface. To do. The CPU 301 controls the drive motor so that the polygon mirror 204 is rotated at a predetermined rotation speed in response to input of image data. When it is determined that the polygon mirror 204 is rotated at a predetermined rotation speed, the CPU 301 determines at least one of the light emission sources 201A, 201B, 201C, and 201D of the semiconductor laser 201 at the timing when the laser beam is incident on the BD 206. Laser light is emitted from one of them. For example, in a state where the polygon mirror 204 is rotating at a constant speed, the CPU 301 continuously turns on the light emission source 201A of the semiconductor laser 201 to generate at least one BD signal. Then, the laser beam is emitted each time a predetermined time elapses from the obtained BD signal so that the laser beam emitted from the semiconductor laser 201A is incident on the BD when reflected by the reflecting surface of the polygon mirror. Then, the CPU 301 causes a counter (not shown) to count a BD signal generated based on the laser light incident on the BD 206. This counter counts from 0 to 4 so as to correspond to the number of reflection surfaces, and when it is counted up to 4, when the next BD signal is counted, the count value is returned to 0.

  At the same time, the CPU 301 is the difference between the output timing of the BD signal generated by the laser beam reflected by a certain surface and the output timing of the BD signal generated by the laser beam reflected by the adjacent surface. A time interval (hereinafter referred to as period data) is acquired. Since the polygon mirror has five reflecting surfaces, the CPU 301 acquires five periodic data and assigns a count value counted by the counter to the five periodic data. Hereinafter, the five period data are represented as T0, T1, T2, T3, and T4. Note that the numbers from T0 to T4 correspond to the count value.

  As shown in Table 2, reference period data Trefa, Trefb, Trefc, Trefd, Tref are assigned to the correction data a, b, c, d, e stored in the memory 304, respectively. The CPU 301 calculates the correlation between the five periodic data acquired above and the five reference periodic data stored in the memory 304 (details will be described later). As described above, a count value is assigned to each of the five period data. The CPU 301 calculates the correlation between the period data obtained from the BD signal and the reference period data, and based on the comparison result of the correlation, a plurality of correction data a, b, c, d, e and the BD signal Correspond with the count value. Thereafter, the CPU reads correction data corresponding to the count value of the BD signal from the memory, and corrects the amount of light with the correction data. For example, it is assumed that a count value 0 is assigned to the correction data a, a count value 1 is assigned to the correction data b, a count value 2 is assigned to the correction data c, a count value 3 is assigned to the correction data d, and a count value 4 is assigned to the correction data e. When the counter counts the BD signal output from the BD as “1”, the CPU reads the correction data b from the memory, and corrects the amount of laser light emitted by the correction data b. Next, since the counter counts the BD signal as “2”, the CPU reads the correction data c from the memory 304. Then, the amount of laser light emitted is corrected by the read correction data c.

  Hereinafter, a method for comparing the correlation between the periodic data obtained from the BD signal and the reference periodic data will be described. In the memory according to the present embodiment, Trefa = 527.481238 (μsec), Trefb = 527.4858679 (μsec), Trefc = 527.43777797 (μsec), Trefd = 527.4468468 (μsec), and Trefe = 52.4952669 (μsec) is stored. These reference cycle data are taken for each polygon mirror when the apparatus is assembled. The data is stored in the memory as reference cycle data. Further, the five period data obtained from the BD signal are T0 = 527.447477 (μsec), T1 = 527.5501468 (μsec), T2 = 527.4952669 (μsec), T3 = 527.473238 (μsec), It is assumed that T4 = 527.473238 (μsec). The image forming apparatus of the present embodiment has a second counter (not shown) that counts the number of reference clock signals from the falling edge to the rising edge of the BD signal, and the CPU 301 calculates the period data from the count value. .

Subsequently, the CPU 301 performs calculations by substituting the values of the reference cycle data Trefa, Trefb, Trefc, Trefd, Tref, and cycle data T0, T1, T2, T3, and T4 into the following calculation formulas 1 to 5. The following five arithmetic expressions are arithmetic expressions for comparing the correlation of each combination of the reference cycle data Trefa, Trefb, Trefc, Trefd, Tref and the cycle data T0, T1, T2, T3, T4. The combination here means a combination of data surrounded by absolute values in the following arithmetic expressions. For example, in the arithmetic expression 1, values are combined such as Trefa and T0, Trefb and T1, Trefc and T2, Trefd and T3, Trefe and T4, and the correlation of the combination is calculated based on the arithmetic expression. The CPU 301 determines that the combination having the smallest value among the calculation results obtained by the following arithmetic expressions is the combination having the highest correlation.
(Calculation Formula 1) = | Trefa−T0 | + | Trefb−T1 | + | Trefc−T2 | + | Trefd−T3 | + | Trefe−T4 |
(Expression 2) = | Trefa−T1 | + | Trefb−T2 | + | Trefc−T3 | + | Trefd−T4 | + | Trefe−T0 |
(Expression 3) = | Trefa−T2 | + | Trefb−T3 | + | Trefc−T4 | + | Trefd−T0 | + | Trefe−T1 |
(Expression 4) = | Trefa−T3 | + | Trefb−T4 | + | Trefc−T0 | + | Trefd−T1 | + | Trefe−T2 |
(Expression 5) = | Trefa−T4 | + | Trefb−T0 | + | Trefc−T1 | + | Trefd−T2 | + | Trefe−T3 |
Substituting each of the reference cycle data and the cycle data into the above formula, (calculation formula 1) = 0.46175 (μsec), (calculation formula 2) = 0.286636 (μsec), (calculation formula 3) = 0 .024 (μsec), (Calculation Formula 4) = 0.128636 (μsec) (Calculation Formula 5) = 0.130175 (μsec). The CPU 301 correlates the combinations of Trefa and T2, Trefb and T3, Trefc and T4, Trefd and T0, and Trefe and T1 based on the calculation result of the calculation formula 3 that has the smallest value among the above five calculation results. Is determined to be the highest. Based on the determination result, the CPU 301 reads the correction data d from the memory 304 when the count value is “0”, and reads the correction data e from the memory 304 when the count value is “1”. When the count value is “2”, the correction data a is read from the memory 304. When the count value is “3”, the correction data b is read from the memory 304. When the count value is “4”, the correction data a is read from the memory 304. Read correction data c.

  Next, a control flow executed by the CPU 301 for performing the above control will be described. First, in response to the input of image data, the CPU 301 associates the count value assigned to the period data with the correction data in the following steps S601 to 606 prior to image formation. When the image data is input, the CPU 301 starts controlling the rotation speed of the polygon mirror 204 so that the rotation speed of the polygon mirror 204 becomes a predetermined speed (step S601). The CPU 301 determines whether or not the polygon mirror 204 is rotating at a predetermined rotation speed based on the signal from the polygon mirror driving unit 307, the period of the BD signal, and the like (step S602). If it is determined in step S602 that the polygon mirror 204 is not rotating at a predetermined rotation speed, the process returns to step S601 to perform acceleration / deceleration control. If it is determined in step S602 that the polygon mirror 204 is rotating at a predetermined rotation speed, the CPU 301 starts counting the BD signal (step S603). The CPU 301 counts the BD signal from 0 to 4, and resets the count value to 0 when the next BD signal is counted when the count reaches 4, and starts counting from 0 again.

  Subsequently, the CPU 301 acquires five period data from the BD signal, and assigns the count value obtained in step S603 to each period data (step S604). For example, the CPU 301 sequentially assigns count values to the cycle data according to the order of the cycle data, such as a count value “0” for the cycle data T0 and a count value “0” for the cycle data T1. .

  Then, the CPU 301 calculates the correlation of a plurality of combinations between the cycle data and the reference cycle data based on the arithmetic expression described above (step S605). The CPU 301 compares the correlation calculated in step S605, and associates the count value of the BD signal with the correction data based on the combination having the highest correlation (step S606). Then, the CPU 301 reads correction data corresponding to the count value from the memory 304, and corrects the light amount based on the read correction data (step S607). Based on the image data, a drive signal is output to the drive unit so as to emit laser light from the light source, and an image is formed (step S608). In step S609, if the CPU 301 determines that the image formation has been completed, the image formation is completed. If the image formation has not been completed, the process returns to step S607 to continue the image formation.

  Next, the period data acquisition method in step S604 will be described with reference to FIG. The polygon mirror 204 is rotated at a substantially constant rotation speed by controlling the acceleration / deceleration of the polygon mirror drive motor 307, but the rotation speed of the polygon mirror 204 is slightly changed. For this reason, if the periodic data is acquired only from the BD signal obtained while the polygon mirror 204 rotates once, the rotational speed fluctuation is included in the periodic data. Therefore, in order to suppress the variation of the periodic data due to the fluctuation of the rotational speed, the periodic data is acquired from the BD signal obtained while the polygon mirror 204 rotates a plurality of times. In this embodiment, an example will be described in which period data is acquired from a BD signal obtained while the polygon mirror 204 rotates 32 times.

  The CPU 301 of the image forming apparatus of this embodiment includes registers 1 to 5 for holding cycle data. First, the CPU 301 clears the registers 1 to 5 (step S701). Then, based on the count value of the BD signal in step S603, the cycle data is added to each of the registers 1 to 5 (step S702). For example, when the count value is “0”, the cycle data corresponding to the count value “0” is added to the register 1. After the polygon mirror makes one rotation, when the counter again counts the BD signal as “0”, the cycle data corresponding to the count value is added to the cycle data held in the register 1. As described above, the period data is added to each of the registers 1 to 5 in accordance with the count value every rotation. Subsequently, the CPU 301 determines whether or not the polygon mirror has rotated 32 times (a predetermined number of rotations) since the input of the period data to the registers 1 to 5 has been started (step S703). In this step, the count value of the BD signal is counted by using the counter 2 for the BD signal after the addition of the period data to the register is started. If the count value A is A <160, the CPU 301 determines that the polygon mirror rotation speed has not reached 32 rotations, and returns to step S702 to continue the control. On the other hand, if the count value is A = 160, the process proceeds to the next step S704. In step S704, the CPU 301 calculates an average value by dividing the addition value of the periodic data stored in the registers 1 to 5 by the rotation number (averaging process). By performing the above control, it is possible to acquire periodic data in which the influence of the variation in the rotational speed of the polygon mirror 204 is reduced.

  As described above, it is possible to suppress the deterioration of the image quality by reading the correction data corresponding to the reflecting surface from the memory 304. However, the use of the above control method for reading correction data from the memory 304 by using the BD cycle may cause the following problems. The scanning optical apparatus 200 has a structure in which the housing 207 is hermetically sealed so that dust is not mixed therein. However, the mixing of dust cannot be completely prevented. As the amount of dust inside the scanning optical device 200 increases with time, the dust is wound up by the air flow generated during rotation, and the dust adheres to the reflecting surface of the polygon mirror 204. The periodic data may not be obtained accurately due to the dirt on the reflecting surface due to the dust. That is, since the BD light reception result is compared to generate a BD signal, the rise and fall of the BD signal change when the BD light reception result changes due to contamination on the reflection surface. As a result, correction data for each reflecting surface may not be determined accurately.

  For example, consider the case where it is desirable to correct the amount of laser light incident on the reflecting surface corresponding to T0 with the correction data c as described above. In this case, the periodic data of the BD signal detected when the reflecting surface of the polygon mirror 204 is dirty are T0 = 527.459797 (μsec), T1 = 527.486468 (μsec), and T2 = 527.5252669 ( μsec), T3 = 527.443238 (μsec), and T4 = 5277.481869 (μsec). The results of the calculation formulas at this time are (calculation formula 1) = 0.176175 (μsec), (calculation formula 2) = 0.156234 (μsec), (calculation formula 3) = 0.104 (μsec), ( Calculation formula 4) = 0.176234 (μsec) (calculation formula 5) = 0.100195 (μsec). The minimum value of the five calculation results is expression 5. Then, although it is desirable to correct the amount of laser light incident on the reflecting surface corresponding to T0 with the correction data c, the CPU 301 calculates the amount of laser light incident on the reflecting surface corresponding to T0 as the correction data e. Will correct it. As described above, there is a possibility that the image quality is deteriorated due to a mismatch between the reflection surface and the correction data.

  In order to solve the above-described problem, the image forming apparatus according to the present exemplary embodiment includes a configuration for updating reference cycle data associated with each of a plurality of correction data. The CPU 301 provided for the image forming measure of the present embodiment stores the periodic data obtained from the BD signal in the memory 304 as new reference data. Thus, even if the reflection surface of the polygon mirror is soiled by updating the reference cycle data, the count value and the correction data can be accurately matched. The timing for updating the reference cycle data may be, for example, when a predetermined number of images are formed immediately after the image forming apparatus is turned on, or after a predetermined time has elapsed since the image formation was completed. In the following, the present embodiment will be described by taking as an example an image forming apparatus that updates reference cycle data and then starts image formation in response to image formation on a predetermined number of recording media.

  FIG. 8 is a control flow executed by the CPU 301 when the reference cycle data stored in the memory 304 is updated. Steps S801 to S806 are the same as steps S601 to S606 in FIG. Note that steps S801 to S806 in the control flow in FIG. 8 are performed simultaneously with the control in steps S601 to S606 in the control flow shown in FIG.

  The CPU 301 assigns the count value to the correction data based on the association between the count value of the BD signal and the correction data performed in step S805, and stores the cycle data acquired in step S804 as new reference cycle data in the memory 304. (Step S807). The CPU 301 ends this control flow in response to the reference cycle data being updated.

  As described above, since the reference cycle data corresponding to the correction data can be updated, the correlation between the reference cycle data and the cycle data is obtained even when the reflection surface of the polygon mirror 204 is dirty. Can be accurately compared. Thereby, even when the reflection surface of the polygon mirror 204 is dirty, it is possible to suppress reading of incorrect correction data from the memory 304.

(Example 2)
In the first embodiment, the configuration in which erroneous correction data is read from the memory 304 by updating the reference cycle data stored in the memory 304 has been described. However, as the stain progresses, the amount of reflected light decreases, and there is a possibility that an image defect such as a decrease in image density occurs. In that case, it is necessary to clean the inside of the scanning optical device including cleaning of the reflection surface of the polygon mirror by a service person or to replace the scanning optical device. The image forming apparatus of the present embodiment compares the reference cycle data stored at the time of shipment from the factory with the updated reference cycle data, and when the difference between the two data exceeds a predetermined value, the scanning optical device is cleaned, or Information for prompting replacement of the scanning optical device is displayed on the display unit. Hereinafter, the configuration will be described.

  FIG. 9 is a block diagram of the image forming apparatus of this embodiment. The difference from the first embodiment is that a memory 901 that is a second memory is provided for a memory 304 that is a first memory. Moreover, the point provided with the operation part 902 also differs from the first embodiment. The memory 304 is a memory that can rewrite data. The memory 901 may be a rewritable memory or a non-rewritable memory. FIG. 10 is a schematic diagram of the operation unit 902. The operation unit 902 includes a display unit 903 and a key input unit 904. The other parts that are the same as those in the first embodiment are denoted by the same reference numerals, and thus detailed description thereof is omitted.

  The memory 901 stores reference cycle data (hereinafter referred to as reference cycle data) stored in the memory 304 at the time of factory shipment. As described in the first embodiment, the reference cycle data stored in the memory 304 is updated, whereas the reference cycle data stored in the memory 901 is updated when the polygon mirror 204 and the scanning optical device 200 are replaced. In principle, it is not updated.

  The CPU 301 calculates the difference between the updated cycle data and the reference cycle data every time the reference cycle data in the memory 304 is updated. When the reflection surface of the polygon mirror 204 becomes dirty, the amount of reflected light decreases, and the difference increases. The difference also increases as the polygon mirror drive motor 307 deteriorates. Therefore, the CPU 301 causes the display unit 903 to display information that prompts replacement or cleaning of the scanning optical device 200 when the calculated difference is equal to or greater than a predetermined value.

The above-mentioned reference cycle data is Td1, Td2, Td3, Td4, and Td5. The CPU 301 substitutes the values of the reference cycle data and the updated reference cycle data into the following calculation formula 6.
(Expression 6) = | Td1-Trefa | + | Td2-Trefb | + | Td3-Trefc | + | Td4-Trefd | + | Td5-Tref |
When the calculation result by the calculation formula 6 does not become a predetermined value or less (predetermined value α or less), the CPU 301 displays the above information on the display unit.

  Hereinafter, the control flow of the present embodiment executed by the CPU 301 will be described with reference to FIG. Steps S1101 to S1107 are the same control flow as steps S901 to S907 in FIG. In step S <b> 1108, the CPU 301 calculates the difference between the updated cycle data and the reference cycle data every time the reference cycle data in the memory 304 is updated based on the calculation formula 6. The difference is compared with a predetermined value α (step S1109), and if it is determined that the difference is larger than the predetermined value α, the CPU 301 displays information for prompting cleaning or replacement of the scanning optical device on the display unit 903 (step S1110). ). After that, the CPU 301 determines whether or not the information displayed on the display unit 903 has been canceled by the user (step S1111). When it is determined that the information displayed on the display unit 903 has been canceled, The image is formed based on (Step S1112). Thereafter, the CPU 301 determines whether or not the image formation based on the input image data has been completed (step S1113). When the image formation has been completed, this control is terminated. On the other hand, if the image formation has not been completed, the process returns to step S1113 to continue the control. On the other hand, if the information displayed on the display unit 903 is not canceled in step S1111, image formation is prohibited and the control is terminated after a predetermined time has elapsed. If it is determined in step S1109 that the difference is smaller than the predetermined value, the CPU 301 advances the control to step S1112 and performs image formation based on the image data.

  Note that the user can easily cancel the display of the information prompting the cleaning or replacement displayed on the display unit 903 by using the key input unit or the like. When the user determines that there is no need to clean or replace the polygon mirror 204, the display can be canceled and image formation can be started.

  In the present embodiment, the reference period data and the reference period data are stored in the memory 304 and the memory 901 at the time of factory shipment, respectively. The embodiment is not limited to this. Periodic data obtained by rotationally driving the polygon mirror when installing the image forming apparatus after shipment from the factory, cleaning the polygon mirror, or replacing the scanning optical apparatus is stored in the memory 304 and the memory 901. May be stored as reference cycle data and reference cycle data. The data stored in the memory 304 and the memory 901 may be stored in one memory.

  In this embodiment, the reference cycle data before being updated and the reference cycle data after being updated are compared, and if the difference between the two data exceeds a predetermined value, the scanning optical device is cleaned or replaced. The configuration for displaying the information for prompting on the display unit has been described. On the other hand, the period data and the reference period data stored in the memory are compared, and if the difference exceeds a predetermined value or the correlation cannot be obtained, cleaning or replacement of the scanning optical device may be promoted. .

  As described above, it is possible to notify the user of information that prompts cleaning or replacement of the polygon mirror by determining the degree of contamination of the polygon mirror using the periodic data of the BD signal.

204 Polygon mirror 301 CPU
305 Laser drive unit 304 Memory

Claims (5)

A photoreceptor,
A light source that emits a light beam to form an electrostatic latent image on the photoreceptor;
A rotating polygon mirror having a plurality of reflecting surfaces; and driving means for rotating the rotating polygon mirror; and rotating the light beam so that the light beam emitted from the light source scans on the photoconductor. Deflection means for deflecting by a polygon mirror;
Detection means for outputting a detection signal in response to receiving the light beam deflected by the rotary polygon mirror;
Correction data for correcting the light amount of the light beam is stored in association with each of the plurality of reference data so that the light beam is emitted from the light source with a light amount corresponding to the reflecting surface on which the light beam is incident. Storage means;
Correlation between periodic data, which is a time interval of a detection signal output from the detection means by receiving the light beam reflected by an adjacent reflection surface among the plurality of reflection surfaces, and the plurality of reference data. Obtaining and correlating the plurality of correction data individually to each of the plurality of reflecting surfaces based on the correlation, and correcting corresponding to the reflecting surface on which the light beam is incident when forming the electrostatic latent image Control means for reading out data from the storage means and correcting the light quantity of the light beam based on the correction data;
Light source driving means for emitting a light beam from the light source with a light amount corrected by the control means based on image data ,
The control means updates the reference data by causing the storage means to store the periodic data output from the detection means based on the correlation so as to correspond to the plurality of reflection surfaces. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the control unit updates the reference data stored in the storage unit when an image is formed on a predetermined number of recording media.   The control means detects whether or not the rotary polygon mirror is rotating at a predetermined rotation speed based on the cycle data, and detects that the rotary polygon mirror is rotating at a predetermined rotation speed. The correlation between the periodic data obtained when the rotary polygon mirror is rotating at a predetermined rotational speed and the reference data stored in the storage means is obtained. Image forming apparatus. A counter for counting the detection signal output by the detection means;
The control means rotates the rotating polygon mirror a plurality of times in order to obtain the periodic data, and each of the reflecting surfaces specified by the counter value obtained by rotating the rotating polygon mirror a plurality of times the image forming apparatus according to the average value of a plurality of said time intervals to claim 2, characterized in that determining said correlation as the period data corresponding to the. Display means for displaying information for prompting replacement of the deflecting means or information for prompting cleaning;
When the difference between the reference data stored in the storage unit and the periodic data is equal to or less than a predetermined value before updating, the control unit is reflected by an adjacent reflection surface among the plurality of reflection surfaces. Further, a correlation between periodic data, which is a time interval of a detection signal output from the detection means by receiving the light beam, and the plurality of reference data is obtained, and each of the plurality of reflecting surfaces is determined based on the correlation. The plurality of correction data are respectively associated with each other, and correction data corresponding to a reflection surface on which the light beam is incident when the electrostatic latent image is formed is read from the storage unit, and based on the correction data, the correction data is read out. Correct the amount of light beam,
The control means, when the difference value between the reference data stored in the storage means and the periodic data before updating is not less than a predetermined value, information that prompts the display means to replace the deflection means , or The image forming apparatus according to claim 1, wherein information prompting cleaning is displayed.

Images