JP5733897B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a technique for performing image forming processing by an electrophotographic method, such as a laser printer or a copying machine.

  In an image forming apparatus using an optical scanning device such as a laser printer or a digital copying machine, a laser beam emitted from a laser diode is reflected by a polygon mirror rotating at a constant speed, whereby a scanning line is formed on a photosensitive drum. Is formed.

  At this time, if the inclination of each reflection surface of the polygon mirror is equal to the rotation axis, the interval between the scanning lines formed by each reflection surface is constant. However, strictly speaking, surface tilt occurs due to a processing accuracy error, and the inclination of each reflection surface of the polygon mirror is not equal to the rotation axis. For this reason, the scanning lines on the photosensitive drum formed by the respective reflective surfaces have variations in the sub-scanning direction, and the intervals between the scanning lines are not constant.

  This variation in the scanning lines is repeated at the rotation cycle of the polygon mirror, so that the density unevenness of the image occurs periodically and becomes visually noticeable. In view of this, there has been proposed a technique for electrically correcting image density unevenness due to variations in scanning line intervals in the sub-scanning direction by detecting the reflection surface of a polygon mirror (Patent Document 1 below).

  According to this conventional technology, a magnet is attached to the lower part of a specific reflecting surface to identify the polygon mirror, the reflecting surface of the polygon mirror is specified by a Hall element located below the polygon mirror, and unevenness of the image is corrected. Like to do.

  Since the tilting of the surface does not usually change with time, it is possible to electrically correct the tilting of the surface by detecting the reflecting surface of the polygon mirror and performing appropriate correction or the like according to each reflecting surface. .

JP 2007-286129 A

  However, in the above-described conventional technology, since the polygon mirror is provided with a detector such as a magnet or a hall element in order to specify the reflecting surface of the polygon mirror, the apparatus configuration and the manufacturing process become complicated, and the cost increases. There is a problem of inviting. Moreover, it is contrary to the request for downsizing of the apparatus and reduction of the number of parts.

  The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to provide an image forming apparatus capable of specifying the reflecting surface of a rotary polygon mirror with a simple configuration and at a low cost. There is to do.

In order to achieve the above object, an image forming apparatus according to the present invention is an emission unit that emits laser light, and a rotary polygon mirror that is rotationally driven. The laser light emitted from the emission means so that a plurality of reflecting surfaces sequentially move on the optical path of the laser light emitted from the emission means, and the laser light emitted from the emission means scans on the photosensitive member. Rotating polygon mirrors that are reflected by the plurality of reflecting surfaces, output means for receiving a laser beam reflected by each reflecting surface of the rotating polygon mirror and outputting a horizontal synchronization signal, and horizontal output from the output means based on the measurement data of the output interval of the synchronizing signal, the generating means for generating periodic data output sequence associates the measurement data, different located on the optical path of the laser beam emitted from said exit means Two identification data associates the one reflection surface of the plurality of reflecting surfaces and the output interval of the two said horizontal synchronizing signal generated by the laser beam is successively reflected by the reflecting surface respectively that, said plurality Storage means stored in association with each of the reflective surfaces, wherein the identification data is stored in association with the order of the plurality of reflective surfaces in the rotation direction of the rotary polygon mirror, and the measurement Based on the result of pattern matching between the periodic data associated with the data output order and the identification data associated with the order of the plurality of reflecting surfaces, among the plurality of reflecting surfaces of the rotary polygon mirror And a specifying means for specifying a reflecting surface on which the laser beam is incident.

  According to the present invention, the reflection surface of the rotary polygon mirror can be specified with a simple configuration and at a low cost.

1 is a cross-sectional view showing an overall configuration of an image forming apparatus according to a first embodiment of the present invention. It is a figure which shows the structure of the exposure control part of an image forming apparatus. It is a block diagram which shows the mechanism for reflective surface specification and surface tilt correction. It is a figure which shows an example of matching with surface ID allocated by the surface identification signal generation part, and BD period measured by the scanning period measurement part in time series. It is a conceptual diagram which shows the correspondence of BD period stored in the scanning period memory | storage part, and surface ID produced | generated by the surface identification signal generation part. It is a conceptual diagram of the BD cycle of each reflective surface of the polygon mirror measured in advance and the corresponding surface tilt correction data stored in the correction data storage unit. It is a figure which shows an example of the BD period stored in the correction data storage part. It is a figure which shows an example of the BD period measured and stored in the scanning period memory | storage part. It is a figure which shows the difference value in each combination pattern when a pattern match is successful. It is a figure which shows the difference value in each combination pattern when pattern matching fails. It is a conceptual diagram which shows an example of the correspondence of the surface ID and BD period in a surface specific part, and the BD period of the correction data storage part of a surface inclination unevenness correction part when a pattern matching is successful. It is a figure which shows an example of matching with the correction | amendment data memorize | stored in the correction | amendment data memorize | stored in the correction | amendment data memory | storage part in the surface ID allocated by the surface identification signal production | generation part, the BD period measured by the scanning period measurement part. It is a flowchart of a process of a reflective surface specification and surface tilt correction. It is a block diagram which shows the mechanism for reflective surface specification and surface tilt correction in 2nd Embodiment. It is a conceptual diagram of the BD period of each reflective surface of a polygon mirror and the surface tilt data corresponding to it stored in the external memory. It is a conceptual diagram which shows a mode that the correction data for each reflective surface of a polygon mirror are produced | generated from the surface tilt data read from the external memory, and are sequentially written in the correction data storage part. FIG. 5 is a conceptual diagram illustrating an example of a correspondence relationship between a surface ID and a BD cycle in a surface specifying unit, a BD cycle and surface tilt data in an external memory, and correction data and a read address in a surface tilt unevenness correction unit when pattern matching is successful. is there. 10 is a flowchart of correction data writing processing. It is a flowchart of the process of reflective surface specification and surface tilt correction in 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a cross-sectional view showing the overall configuration of the image forming apparatus according to the first embodiment of the present invention. The image forming apparatus includes a document conveying unit 130, a document reading unit 120, an image forming unit 100, and the like.

  The document conveying unit 130 is configured as follows. The documents set on the document table 131 are conveyed one by one to the document reading position by the sheet feeding roller 132. At the original reading position, the original is placed at a predetermined position by the original conveying belt 137 driven by the motor 136, and the original reading operation is performed by the original reading unit 120. After the original reading operation, the conveyance path is changed by the flapper 135, and the motor 136 is reversed to discharge the original to the discharge tray 138 by the discharge roller 134.

  The document reading unit 120 is configured as follows. The exposure lamp 122 includes a fluorescent lamp, a halogen lamp, and the like, and irradiates a document on a document placement glass (document table) 126 while moving in a direction perpendicular to the longitudinal direction. Scattered light from the document due to irradiation of the exposure lamp 122 is reflected by the first mirror table 121 and the second mirror table 123 and reaches the lens 124. At this time, the second mirror stage 123 moves at a half speed with respect to the movement of the first mirror stage 121, and the distance from the irradiated original surface to the lens 124 is always kept constant. The first mirror base 121 and the second mirror base 123 are moved by a motor 125. An image on the original is formed on a light receiving portion of a CCD line sensor 127 in which thousands of light receiving elements are arranged in a line via mirror bases 121 and 123 and a lens 124, and the CCD line sensor 127 sequentially forms a line. It is photoelectrically converted in units. The photoelectrically converted signal is processed by a signal processing unit (not shown), PWM-modulated and output.

  The image forming unit 100 is configured as follows. The image forming unit 100 includes an exposure control unit 200. The exposure control unit 200 drives the semiconductor laser 101 that is an emission unit based on the PWM-modulated image signal that is the output of the signal processing unit, and the light beam is applied to the surface of the photoreceptor 107 that is rotating at a constant speed. Eject. At this time, the light beam is deflected and scanned using the polygon mirror 102 which is a rotating polygon mirror which is rotated by the motor 103 in parallel with the axial direction of the drum-shaped photoconductor 107. Note that before the light beam is emitted, the remaining charge on the drum is neutralized by a pre-exposure lamp (not shown), and the surface of the photoconductor 107 is uniformly charged by a primary charger (not shown). Accordingly, the photosensitive member 107 receives the light beam while rotating, thereby forming an electrostatic latent image on the drum surface. Then, the electrostatic latent image on the drum surface is visualized with a developer (toner) of a predetermined color by the developing device 104.

  Transfer paper transported from transfer paper feed stages 140, 150, 160, 170, 180 described later is transported to the registration roller 106. The registration roller 106 detects the arrival of the transfer paper using the sensor 105, and feeds the transfer paper to the transfer position in accordance with the timing of the leading edge of the image formed on the photoconductor 107 and the leading edge of the transfer paper. The transfer charger 108 transfers the developed toner image on the photoconductor 107 onto the fed transfer paper. After the transfer, the remaining toner is removed from the photoconductor 107 by a cleaner (not shown). The transfer paper that has been transferred is easily separated from the photoconductor 107 because of the large curvature of the photoconductor 107, but further, by applying a voltage to a static elimination needle (not shown), the adsorption force between the photoconductor 107 and the transfer paper. To make it easier to separate.

  The separated transfer paper is sent to the fixing unit 109 to fix the toner. The fixing unit 109 includes a ceramic heater 110, a thin film 111, and a roller. The heat of the ceramic heater 110 is efficiently transmitted through the film 111. The cooling roller radiates heat from the fixing unit roller. The feeding roller is composed of one large roller and two small rollers, and feeds the transfer paper from the fixing unit 109 and corrects the curl of the transfer paper.

  The direction flapper 112 switches the discharge destination of the transfer paper to the tray 114 and the transport unit 190 according to the operation mode.

  The transport unit 190 is configured as follows. A unit for transporting transfer paper to a post-processing apparatus 10 described later, and transports the transfer paper by transport rollers 191.

  The transfer paper feed stages 140, 150, 160, and 170 are main body feed stages, and are configured by the same mechanism. The transfer paper feed stage 180 is a deck paper feed stage that can store a larger amount of transfer paper than the transfer paper feed stages 140, 150, 160, and 170. Since the transfer paper feed stages 140, 150, 160, and 170 have almost the same configuration, the configuration will be described using the transfer paper feed stage 140 as an example.

  In the transfer paper feeding stage 140, a bottom plate 142 that is moved up and down by a lift-up motor 143 is disposed on the bottom surface of the cassette 141 that stores and stores the transfer paper. When the bottom plate 142 is raised, the transfer paper can be waited at a predetermined standby height. The transfer paper waiting at a predetermined position is conveyed to the paper feed roller pair 145 using the pickup roller 144. The pair of paper feed rollers 145 are torqued in the reverse rotation direction to the paper feed, thereby feeding the transfer sheets one by one to the transport path while preventing the transfer paper as a recording medium from being double fed. The transport rollers 146 are a pair of rollers for transporting the transfer paper transported from the paper feed stage below the transfer paper feed stage 140 further upward.

  The cassettes 151, 161, 171, the bottom plates 152, 162, 172, and the lift-up motors 153, 163, 173 are configured similarly to the cassette 141, the bottom plate 142, and the lift-up motor 143, respectively. The pickup rollers 154, 164, 174, the paper feed roller pairs 155, 165, 175, and the transport rollers 156, 166, 176 are configured in the same manner as the pickup roller 144, the paper feed roller pair 145, and the transport roller 146, respectively.

  The transfer paper feed stage 180, which is a deck paper feed stage, is configured as follows. A bottom plate 182 for raising the transfer paper to the standby position is disposed on the bottom surface of the paper storage 181 for storing and storing the transfer paper. The bottom plate 182 is connected to a belt that is rotated by a motor 183, and the raising and lowering of the bottom plate 182 is controlled by the movement of the belt. The transfer paper at the standby position is conveyed to the paper feed roller pair 184 by the pickup roller 185, and the transfer paper is conveyed to the conveyance path while preventing double feeding as in the case of main body paper feeding.

  The post-processing device 10 is configured as follows. Transfer paper from the image forming unit 100 is received by the roller 11 into the post-processing apparatus 10. When the tray 14 is selected as the output destination of the received transfer paper, the transport direction is switched by the flapper 12 and the transfer paper is discharged to the tray 14 using the roller 13. The tray 14 is a discharge tray used for temporary use such as a discharge destination of processing that is interrupted during normal processing.

  The trays for normal discharge are the tray 18 and the tray 19. These trays can be discharged by switching the transport path downward by the flapper 12 and then selecting the transport path toward the roller 16 by the flapper 28. When the conveyance path is selected vertically downward by the flapper 28 and the flapper 29 and the conveyance direction is reversed by the reverse roller 15, the reverse discharge can be performed. When discharging to the trays 18 and 19, stapling using the stapler 17 is possible. Whether the transfer paper is output to the tray 18 or the tray 19 is determined by moving the tray itself up and down using the shift motor 20.

  The tray 27 is a discharge tray used for bookbinding. The transfer paper is conveyed from the reversing roller 15 to the roller 21, and a predetermined amount of transfer paper is stored in the primary storage unit 23. After the accumulation, the bookbinding operation is performed with the stapler 24, the direction of the flapper 25 is changed, the roller 22 is rotated in the direction opposite to that during accumulation, and the sheet is discharged to the tray 27 via the roller 26.

  FIG. 2 is a diagram illustrating a configuration of the exposure control unit 200 of the image forming apparatus. In the exposure control unit 200, the laser drive unit 202 receives an image signal from the image signal generation unit 201, and the laser drive unit 202 generates a laser drive signal. Laser light is emitted from the semiconductor laser 101 based on the laser drive signal. Here, the semiconductor laser 101 includes a laser capable of emitting a plurality of lasers.

  Since the laser light emitted by the semiconductor laser 101 is diffusely radiated, it is converted into parallel light through the collimator lens 203 and enters the polygon mirror 102. The polygon mirror 102 has a regular pentagonal shape when viewed in the direction of the rotation axis, and has a plurality of reflecting surfaces that are mirror surfaces. In the second embodiment, the polygon mirror 102 having five reflecting surfaces is shown as an example, but the number of reflecting surfaces is not limited. The polygon mirror 102 rotates at an equiangular speed, and the laser light incident on the polygon mirror 102 is reflected by the reflecting surface that receives the laser light and becomes reflected light. Accordingly, the angle of the reflected light changes as the polygon mirror 102 rotates.

  The reflected light has its scanning speed corrected through the f-θ lens 204 and scans the surface of the photoconductor 107 at a constant speed. The BD sensor 205 is a sensor that detects reflected light from the polygon mirror 102. When detecting reflected light, the BD sensor 205 as output means generates and outputs a beam detect (hereinafter referred to as BD) signal that is a horizontal synchronization signal for synchronizing the rotation of the polygon mirror 102 and the image signal. The BD signal is also a scanning start position signal.

  Hereinafter, the process of specifying the reflecting surface and correcting the surface tilt in the present embodiment will be described.

  FIG. 3 is a block diagram illustrating a mechanism for reflecting surface specification and surface tilt correction. In addition to the exposure control unit 200, this mechanism includes a surface specifying unit 300 and a surface tilt unevenness correcting unit 400. The operations of the surface specifying unit 300 and the surface tilt unevenness correcting unit 400 are controlled by a control signal from a CPU (specification unit, control unit) 600.

  The image signal generation unit 201 generates an image signal and supplies it to the laser driving unit 202. The laser driving unit 202 outputs laser light from the semiconductor laser 101 in accordance with the supplied image signal and correction data described later. The laser light emitted from the semiconductor laser 101 is reflected by the reflecting surface of the polygon mirror 102 that rotates at a constant angular velocity, and the reflected laser light is detected by the BD sensor 205 and then scanned on the photoconductor 107. Here, when the laser beam is detected by the BD sensor 205, a BD signal is generated and output.

Face identifying unit 300 includes scanning period measuring unit 3 01, the scanning period storage section 302, a surface identification signal generator 303. When the polygon mirror 102 stably rotates at a constant speed and the surface identification process is started, the surface identification signal generation unit 303 assigns ID1 as a surface ID that is a surface identification signal to the current reflection surface, and thereafter Each time a BD signal is input, the surface ID is updated and assigned to the next reflecting surface.

  The “current reflection surface” is a reflection surface that supplies reflected light that is the source of the BD signal output immediately before. Each time the polygon mirror 102 makes one rotation, that is, every time the BD signal is output by the same number as the number of reflection surfaces (five), the same reflection surface becomes the source of the reflected light. In this example, each BD signal output once every five times corresponds to a certain reflecting surface. Therefore, the surface ID identifies each reflection surface and also identifies each BD signal in one rotation of the polygon mirror 102.

  In the scanning period measurement unit 301, an “BD period” that is an output interval of the BD signal is detected as an output interval for each reflection surface by an internal counter. Therefore, the BD period is measured by the number of faces of the polygon mirror 102. Then, the BD cycle of each reflecting surface is stored in the scanning cycle storage unit 302 in the order of measurement. The reflection surface corresponding to the BD signal on the start side of the BD period measured first is not fixed and can be different each time.

  For example, as shown in FIG. 4, in the case where the polygon mirror 102 has five reflecting surfaces A to E, after the start of the surface identification, the laser beam is reflected at a position immediately after the first BD signal is output. It is assumed that the reflection surface located is the D surface. In this case, the surface identification signal generation unit 303 assigns the surface ID “ID1” to the D surface. When the next (second) BD signal is input, an interval from the first BD signal is measured by the scanning cycle measuring unit 301, and this is stored in the scanning cycle storage unit 302 as β1 which is the BD cycle of the D plane. Store.

  When the next (third) BD signal is further input, the interval from the immediately preceding (second) BD signal is measured as the BD period of the next E plane, and the BD period β2 is stored in the scanning period storage unit 302. While storing, “ID2” is assigned to the E plane as the plane ID. Such processing is performed for the number of surfaces of the polygon mirror 102, and the BD periods β (β1 to β5) of the respective reflecting surfaces are stored in the scanning period storage unit 302, and at the same time, the surface IDs (ID1 to ID5) are assigned. FIG. 5 shows a correspondence relationship between the BD period β stored in the scanning period storage unit 302 and the surface ID generated by the surface identification signal generation unit 303.

  As illustrated in FIG. 3, the surface tilt unevenness correction unit 400 includes a correction data storage unit (storage unit, storage unit) 401 and a correction data control unit (readout unit) 402. As shown in FIG. 6, the correction data storage unit 401 stores the BD cycle α (α1 to α5) of the respective reflection surfaces of the A surface to E surface of the polygon mirror 102 and the corresponding surface tilt correction data data ( data1 to data5) are stored in association with each other.

  Here, the BD cycle α is a parameter corresponding to the BD cycle β, which is measured in advance by specifying each of the reflection surfaces A to E. However, which reflective surface corresponds to each of the BD cycles β1 to β5 can be changed in each surface specification, and which BD cycle α1 to α5 corresponds to which BD cycle β will be described later. It is not determined that the reflection surface specific processing is not performed.

  The BD cycle α can be measured by the same method as the BD cycle β, but the measurement method is not limited. That is, since it is assumed that the measurement is performed at the stage before shipment of the image forming apparatus, it is not essential to perform an operation of actually scanning by rotating the polygon mirror 102. The surface tilt correction data data (hereinafter, also simply referred to as “correction data data”) is data for correcting the surface tilt amount of each reflecting surface measured in advance at the time of image formation. It is assumed that this data is also measured at a stage before the shipment of the device.

  The correction data control unit 402 outputs a read address adrs to the correction data storage unit 401 according to the surface ID generated by the surface identification signal generation unit 303 of the surface specifying unit 300 according to the control by the CPU 600. Then, the correction data data stored in the read address adrs is received from the correction data storage unit 401 and the correction data is output to the laser driving unit 202.

  Next, a method for associating the surface ID generated by the surface specifying unit 300 with the read address adrs stored in the correction data storage unit 401 will be described.

  The CPU 600 reads the BD cycle (β1 to β5) from the scanning cycle storage unit 302 of the surface specifying unit 300 and reads the BD cycle (α1 to α5) from the correction data storage unit 401. Then, the read BD period (β1 to β5) and the BD period (α1 to α5) are compared, and the correction data data in the correction data storage unit 401 is compared with the surface ID of each reflection surface of the polygon mirror 102. A read address adrs is set.

  For example, when the polygon mirror 102 has a five-surface configuration, the sum of squares of the differences between the BD period (β1 to β5) and the BD period (α1 to α5) is obtained for each of the five types of combination patterns as follows. First, when a BD signal is output for the first time in the surface specifying process, a reflection surface at a position where the laser beam is reflected is arbitrarily determined. This arbitrarily defined reflecting surface is defined as a first surface (surface ID = ID1), each reflecting surface ordered in the order of appearance along the rotation direction of the polygon mirror 102, and each reflecting surface sequentially ordered from the A surface in advance. Are combined in the order as a first combination pattern.

  Each set in the first combination pattern (here, a set of the first surface and the A surface, a set of the second surface and the B surface, a set of the third surface and the C surface, a set of the fourth surface and the D surface, A process of calculating the square of the difference between the BD period β and the BD period α is executed for the fifth surface and the E surface). When the combination patterns are changed by shifting the pre-ordered reflective surfaces one by one, there are five types of combination patterns. The process of calculating the square of the difference is performed for each group in all five combination patterns. For example, in the second combination pattern, the first surface and B surface group, the second surface and C surface group, the third surface and D surface group, the fourth surface and E surface group, the fifth surface And the A plane set.

Then, for all the combination patterns, the sum of the squares of the differences of the respective groups (that is, the sum of squares of the differences) is obtained and set as the difference value. The difference values 1 to 5 of the combination patterns 1 to 5 are specifically calculated by the following calculation formula.
Pattern 1: (β1-α1) ² + (β2-α2) ² + (β3-α3) ² + (β4-α4) ² + (β5-α5) ² = difference value 1
Pattern 2: (β1-α2) ² + (β2-α3) ² + (β3-α4) ² + (β4-α5) ² + (β5-α1) ² = difference value 2
Pattern 3: (β1-α3) ² + (β2-α4) ² + (β3-α5) ² + (β4-α1) ² + (β5-α2) ² = difference value 3
Pattern 4: (β1-α4) ² + (β2-α5) ² + (β3-α1) ² + (β4-α2) ² + (β5-α3) ² = difference value 4
Pattern 5: (β1-α5) ² + (β2-α1) ² + (β3-α2) ² + (β4-α3) ² + (β5-α4) ² = difference value 5
In addition, when changing a combination pattern, the order which changes the combination of BD period (alpha) and BD period (beta) is not ask | required. For example, the BD cycle β may be shifted one by one with respect to the BD cycle α.

  FIG. 7 is a diagram illustrating an example of the BD cycle (α1 to α5) stored in the correction data storage unit 401. FIG. 8 is a diagram illustrating an example of a BD cycle (β1 to β5) measured and stored in the scanning cycle storage unit 302. The numerical value of the BD period on the vertical axis in FIG. 8 is the counter value of the counter inside the scanning period measuring unit 301, and the numerical value in FIG. FIG. 8 shows an example in which the D surface is the first surface (surface ID = ID1).

  Here, the correspondence of each BD cycle α in the correction data storage unit 401 to each BD cycle β in the scanning cycle storage unit 302 is determined by a combination pattern having a minimum difference value among the five combination patterns. At that time, a certain threshold value (see FIGS. 9 and 10) is set, and satisfaction of the matching condition that “the minimum difference value is equal to or less than the threshold value and all other difference values are greater than the threshold value” is determined. Only when this matching condition is satisfied, it is determined that the association (pattern matching) of each BD cycle α in the correction data storage unit 401 with each BD cycle β in the scanning cycle storage unit 302 has succeeded.

  Here, the surface identification unit 300 associates the surface ID with the BD cycle β (see FIG. 5). On the other hand, in the correction data storage unit 401, the read address adrs in which the correction data data is stored and the BD cycle α are associated with each other, and the BD cycle α and the correction data data have a corresponding relationship through the read address adrs. (See FIG. 6).

  When the pattern match is successful, it corresponds to the surface ID of each reflection surface in the correction data data of the correction data storage unit 401 based on the one-to-one correspondence between the BD period β and the BD period α in the combination pattern. Use what you have done to correct the tilt. That is, the read address adrs corresponding to the surface ID is acquired in the order of surface ID → BD cycle β → BD cycle α → read address adrs (see FIG. 11). Then, the correction data “data” stored at this address “adrs” is read out as correction data used for the surface tilt correction.

  Since the correspondence relationship between the BD cycle β and the BD cycle α is found, it is also found which reflection surface is actually the reflecting surface currently reflecting the laser beam. That is, in the stage before the completion of the surface specification, only the surface ID is assigned to each reflective surface of the polygon mirror 102, and the absolute position of each reflective surface is not actually known. However, after the surface specification is completed, each of the plurality of reflection surfaces of the polygon mirror 102 is specified. Therefore, from the correspondence relationship with the BD signal, the result of specifying whether each reflecting surface is a reflecting surface reflecting the laser beam or at which relative position is the reflecting surface with respect to the reflecting surface. can get.

  On the other hand, if it is determined that the pattern match has failed, for example, the correction data data in the correction data storage unit 401 is averaged regardless of the surface ID, and the same correction data is used for all the reflective surfaces. Make the same correction. Therefore, the reflection surface is not specified.

  Suppose that when pattern matching fails, a pattern having the smallest minimum difference value is regarded as a successful pattern and correction is performed. Then, when the sub-scanning pitch becomes dense, the place where the laser light quantity should be lowered may be increased, or when the sub-scanning pitch becomes sparse, the place where the laser light quantity should be raised may be lowered. In such a case, the correction data data corresponding to the surface ID is not adopted because it may be conspicuous on the contrary rather than correcting the pitch unevenness of the sub-scanning.

  Therefore, when pattern matching fails, the same correction data is used for each surface ID without correcting the reflecting surface corresponding to each surface ID, and unevenness when pattern matching fails is determined. Control to keep to a minimum. Here, the same correction data may be predetermined data instead of the average value.

  If the pattern match is successful, the minimum difference value approaches zero as much as possible. Therefore, as a method of determining the threshold value T in the above matching condition, it is desirable to set an error value calculated from rotation jitter of the polygon mirror 102 or the like when pattern matching is successful.

  For example, as shown in FIG. 9, the difference value 4 that is the smallest difference value is equal to or less than the threshold T, and the difference value 1, the difference value 2, the difference value 3, and the difference value 5 other than the smallest difference value 4 are all. If it is greater than the threshold T, it is considered that the pattern match has succeeded.

  On the other hand, as shown in FIG. 10, when all the difference values are larger than the threshold value T, it is considered that the pattern matching has failed. This may occur when, for example, noise enters the BD signal, the BD cycle of a certain reflecting surface cannot be accurately measured in the scanning cycle storage unit 302.

  For example, when the difference value 4 takes the minimum value and the pattern matching is successful, as shown in FIG. 11, the BD cycle of the correction data storage unit 401 corresponding to the BD cycle β1 of the scanning cycle storage unit 302 is the BD cycle α4. It becomes. Referring to FIGS. 7 and 8, the transition pattern of BD cycle β starting from the reflective surface (D surface) corresponding to BD cycle β1 in FIG. 8 and the reflective surface corresponding to BD cycle α4 in FIG. It can be seen that the transition pattern of the BD period α starting from (D plane) is the most approximate. Eventually, the pattern match is to specify the starting points of the BD periods such that the transition pattern of the BD period β matches the transition pattern of the BD period α.

  In this case, “adrs4” is set as the read address adrs in the correction data storage unit 401 of the surface tilt unevenness correction unit 400 for ID1 which is the surface ID corresponding to the BD cycle β1. In the surface tilt correction, the correction data data4 stored in the read address adrs4 is read and used as correction data.

As described above, when the correspondence between the surface ID and the read address adrs in the correction data storage unit 401 is determined, the correction data corresponding to the current reflection surface of the polygon mirror 102 according to each surface ID as shown in FIG. It is possible to read and use data. In the surface tilt correction, the laser driving unit 202 controls the emission of laser light according to the read correction data data, specifically, adjusts the laser light quantity. As a result, the density unevenness of the image due to the tilting of the polygon mirror 102 can be corrected.

  In the following, a description will be given of control processing for reflecting surface specification and surface tilt correction by the CPU 600. FIG. 13 is a flowchart of the process of specifying the reflecting surface and correcting the surface tilt.

  First, in step S101, the CPU 600 determines whether or not image formation is started. If image formation is started, the process proceeds to step S102 to determine whether or not the rotation of the polygon mirror 102 is stable. Then, when the rotation of the polygon mirror 102 is stabilized, the CPU 600 advances the process to step S <b> 103, and controls the scanning cycle measuring unit 301 to measure the BD cycle β and store it in the scanning cycle storage unit 302. When the measurement of the BD period β is completed for all the reflection surfaces of the polygon mirror 102, the CPU 600 advances the process to step S104. In step S <b> 104, the CPU 600 reads out the BD cycle β of each reflecting surface of the polygon mirror 102 from the scanning cycle storage unit 302.

  Next, in step S <b> 105, the CPU 600 reads out the BD cycle α of each reflecting surface of the polygon mirror 102 from the correction data storage unit 401. Next, in step S106, the CPU 600 calculates a difference value in each combination pattern for the number of faces of the polygon mirror 102 from the read BD period β and BD period α of each reflecting surface. For example, when there are five polygon mirrors 102, since there are five combinations of BD periods, difference value 1 to difference value 5 are calculated.

  Next, in step S107, the CPU 600 performs a pattern match between the BD cycle α and the BD cycle β in accordance with the matching condition described above, and determines whether the pattern match is successful. As a result, if the pattern match is successful, the CPU 600 advances the process to step S108.

  In step S108, the CPU 600 identifies the combination pattern that has the minimum difference value, and grasps the one-to-one correspondence between the BD period β and the BD period α in the combination pattern. Then, as described above, the CPU 600 follows the correspondence relationship and sets the read address adrs in the correction data storage unit 401 for each surface ID (see FIG. 11).

  Next, in step S109, the CPU 600 controls the correction data control unit 402 to read out the correction data data stored in the read address adrs set for each surface ID from the correction data storage unit 401 (see FIG. 12). ). Further, the CPU 600 controls the correction data control unit 402 to output the correction data data to the laser driving unit 202. As a result, correction data data is set for correcting the laser beam for each reflecting surface of the polygon mirror 102, and the laser light quantity is adjusted.

  On the other hand, if the pattern match fails in step S107, the CPU 600 advances the process to step S111. In step S111, the CPU 600 sets the average value of the correction data “data” stored in the correction data storage unit 401 as common correction data for all the surface IDs. Then, the same correction is performed on the laser light with respect to each reflecting surface of the polygon mirror 102.

  In subsequent step S110, CPU 600 forms an image. In step S112, the CPU 600 determines whether or not the image formation is completed, and ends the control process when the image formation is completed.

  According to the present embodiment, a combination pattern of the BD period β corresponding to each surface ID stored in the scanning period storage unit 302 by measurement and the BD period α of each reflecting surface of the polygon mirror 102 measured in advance. The reflection surface of each surface ID is specified by the match. Since there is no need to provide a dedicated component such as a magnet or Hall element for specifying the reflecting surface, it is possible to specify a plurality of reflecting surfaces of the polygon mirror 102 with a simple configuration and at low cost. It also responds to requests for downsizing of equipment and reduction in the number of parts.

  When the reflection surface is specified, the read address adrs of the surface tilt correction data data in the correction data storage unit 401 is set for each surface ID. Then, using the correction data data stored in the read address adrs set for each surface ID, the laser light quantity for the reflecting surface corresponding to each surface ID is adjusted. Thereby, it is possible to appropriately correct the unevenness of the image due to the surface tilt of each reflecting surface.

  If the pattern matching fails, the laser light emission is controlled using the common correction data, so that it is possible to prevent the unevenness of the image from increasing due to inappropriate correction.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS. In particular, FIGS. 14, 17, and 19 correspond to FIGS. 3, 11, and 13, respectively.

  FIG. 14 is a block diagram showing a mechanism for reflecting surface specification and surface tilt correction in the second embodiment. This mechanism is different from the mechanism of the first embodiment (FIG. 3) in that an external memory 500 is added, and the other configurations are the same as those of the first embodiment. The difference from the first embodiment will be mainly described.

  FIG. 15 is a conceptual diagram of the BD cycle α of each reflecting surface of the polygon mirror 102 and the corresponding surface tilt data. In the external memory 500, a BD cycle α (α1 to 5) as shown in FIG. 15 and face-down data DATA (DATA1 to 5) are stored in association with each other. These data are preliminarily measured at a factory or the like before shipment of the image forming apparatus, and are assumed to be delivered with the apparatus.

  In the image forming apparatus after delivery, when the power is turned on, the CPU 600 controls the surface tilt data DATA of each reflecting surface of the polygon mirror 102 from the external memory 500 to the surface tilt unevenness correction unit 400 as shown in FIG. Is read out. Then, correction data data for each reflecting surface is generated from the read surface tilt data DATA, and the correction data data is written in the correction data storage unit 401 in the order of reading the surface tilt data DATA. As a result, as in the first embodiment, the correction data data1 to 5 are stored in the read addresses adrs1 to 5, respectively.

  Here, the correspondence relationship between the read addresses adrs1 to 5 of the face-down data DATA1 to 5 stored in the correction data storage unit 401 and the BD cycles α1 to 5 stored in the external memory 500 can be understood. ing. The method for maintaining the correspondence relationship is not limited. For example, some information for association, such as information on the order of generation of the correction data data, is stored in the correction data storage unit 401. As a result, as in the first embodiment, the read address adrs, the correction data data, and the BD cycle α are associated with each other.

  The CPU 600 reads the BD cycle (β1 to β5) from the scanning cycle storage unit 302 of the surface specifying unit 300 and reads the BD cycle (α1 to α5) from the external memory 500. Then, the read BD period (β1 to β5) and the BD period (α1 to α5) are compared, and the surface tilt correction data in the correction data storage unit 401 is compared with the surface ID of each reflection surface of the polygon mirror 102. A data read address adrs is set.

  The mode of association (pattern matching) between the BD cycle β and the BD cycle α is the same as in the first embodiment, and is performed using the calculation formula and the threshold value T.

  When the pattern match is successful, it corresponds to the surface ID of each reflection surface in the correction data data of the correction data storage unit 401 based on the one-to-one correspondence between the BD period β and the BD period α in the combination pattern. Use what you have done to correct the tilt. This is the same as in the first embodiment.

  For example, when the difference value 4 takes the minimum value and the pattern matching is successful, as shown in FIG. 17, the BD cycle of the external memory 500 corresponding to the BD cycle β1 of the scanning cycle storage unit 302 becomes the BD cycle α4. . Therefore, “adrs4” which is the read address adrs of the correction data storage unit 401 in the surface tilt unevenness correction unit 400 corresponding to the BD cycle α4 is set for ID1 which is the surface ID corresponding to the BD cycle β1. In the surface tilt correction, the correction data data4 stored in the read address adrs4 is read and used as correction data.

  On the other hand, if the pattern match fails, as in the first embodiment, the average value of the correction data data in the correction data storage unit 401 is used as common correction data, which is the same as the laser beam for each reflecting surface. Perform the correction.

  Hereinafter, control processing for reflecting surface specification / surface tilt correction by the CPU 600 in the present embodiment will be described.

  FIG. 18 is a flowchart of the correction data writing process. This process is executed when the apparatus is turned on.

  When the power is turned on, the CPU 600 sequentially reads surface tilt data DATA of each reflecting surface of the polygon mirror 102 from the external memory 500 in step S201. Next, in step S202, the CPU 600 generates correction data data from the surface tilt data DATA of each reflecting surface. Next, in step S <b> 203, the CPU 600 writes the correction data data in the correction data storage unit 401 in the order of generation.

  FIG. 19 is a flowchart of the process of specifying the reflection surface and correcting the surface tilt according to the second embodiment. The process of FIG. 18 may be executed once prior to the process of FIG.

  In the process of FIG. 19, the CPU 600 first executes a process similar to steps S101 to S104 of FIG. Next, in step S <b> 301, the CPU 600 reads out the BD cycle α of each reflecting surface of the polygon mirror 102 from the external memory 500. Thereafter, the same processing as steps S106 to S112 in FIG. 13 is executed.

  According to the present embodiment, the specification of the reflecting surface is realized with a simple configuration and at a low cost, and with respect to appropriately correcting the unevenness of the image due to the surface tilt of each reflecting surface, the first embodiment and Similar effects can be achieved.

  Incidentally, the external memory 500 may be provided as an EEPROM or the like inside the laser scanner unit including the exposure controller 200. By doing so, it is possible to measure and store the surface tilt data DATA of the reflecting surface of the polygon mirror 102 in each laser scanner unit in advance in a factory or the like. Accordingly, there is an advantage that when the laser scanner unit is replaced after delivery of the apparatus, the new laser scanner unit and the reflection surface data DATA of the reflecting surface can be accurately aligned.

  In each of the above embodiments, the BD cycle, which is the output interval of the BD signal, is measured as the counter value of the counter, but may be measured in units of time.

  Further, the mode of controlling the emission of the laser light after specifying the reflection surface is not limited to the control of the light amount of the laser light, and any mode that corrects the unevenness of the image due to the surface tilt may be used. For example, as disclosed in Patent Document 1, a light source that is most suitable for correcting the tilting of each reflecting surface among a plurality of light sources may be selected.

DESCRIPTION OF SYMBOLS 101 Semiconductor laser 102 Polygon mirror 107 Photoconductor 205 BD sensor 301 Scan period measurement part 401 Correction data storage part 402 Correction data control part 600 CPU

Claims (6)

Injection means for emitting laser light;
A rotary polygon mirror that is rotationally driven and has a plurality of reflection surfaces, and the plurality of reflection surfaces are sequentially moved on an optical path of laser light emitted from the emission means by being driven to rotate, and the emission A rotating polygon mirror that reflects the laser light emitted from the emitting means by the plurality of reflecting surfaces so that the laser light emitted from the means scans the photosensitive member;
An output means for receiving a laser beam reflected by each reflecting surface of the rotary polygon mirror and outputting a horizontal synchronization signal;
Generating means for generating period data in which the output order of the measurement data is associated based on the measurement data of the output interval of the horizontal synchronization signal output from the output means;
The output interval of the two horizontal synchronization signals generated by the laser beams sequentially reflected by each of the two different reflecting surfaces positioned on the optical path of the laser beam emitted from the emitting means and the plurality of reflecting surfaces Storage means for storing identification data associated with one reflective surface in association with each of the plurality of reflective surfaces, wherein the identification data is the plurality of reflective surfaces in the rotation direction of the rotary polygon mirror. Storage means stored in association with the order of
The plurality of reflecting surfaces of the rotary polygon mirror based on the result of pattern matching between the periodic data associated with the output order of the measurement data and the identification data associated with the order of the plurality of reflecting surfaces An image forming apparatus comprising: a specifying unit that specifies a reflection surface on which the laser beam is incident.   Storage means for storing the correction data for correcting the surface tilt of each reflecting surface of the rotary polygon mirror in association with each reflecting surface, and according to the result of specifying the reflecting surface by the specifying means, each reflecting surface A reading means for reading out corresponding correction data from the storage means, and a control means for controlling the emission of the laser beam by the emission means based on the correction data read by the reading means. Item 2. The image forming apparatus according to Item 1.   Prior to the specification of the reflecting surface by the specifying means, the control means reads the surface tilt data from an external memory storing the surface tilt data of the respective reflecting surfaces of the rotary polygon mirror, and reads the surface tilt data from the read surface tilt data. The image forming apparatus according to claim 2, wherein correction data is generated and stored in the storage unit in correspondence with each of the reflecting surfaces.   4. The image forming apparatus according to claim 2, wherein the control unit adjusts the amount of laser light emitted by the emission unit for each of the reflection surfaces based on the read correction data. .   The specifying means includes, as a first surface, a reflecting surface that is arbitrarily determined among the reflecting surfaces of the rotating polygon mirror, the reflecting surfaces that are ordered along the rotating direction of the rotating polygon mirror, and the rotating direction of the rotating polygon mirror. A process of calculating the square of the difference between the period data and the identification data is performed for each set in the combination pattern obtained by combining the reflecting surfaces sequentially ordered along the order, and this process is performed. The pre-ordered reflecting surfaces are shifted one by one to change the combination pattern, and all the combination patterns are performed.From the combination pattern that minimizes the sum of the squares of the differences of each set, the laser light is The image forming apparatus according to claim 1, wherein an incident reflection surface is specified.   The specifying means is such that only the sum of the squares of the differences of each set in a certain combination pattern is equal to or less than a threshold, and the sum of the squares of the differences of each set in another combination pattern is greater than the threshold. The reflective surface on which the laser beam is incident is specified from the certain one combination pattern only when the above condition is satisfied. In other cases, the reflective surface on which the laser beam is incident is not specified. The image forming apparatus according to claim 5.