JP4764116B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine, and more particularly to an image forming apparatus that corrects a scanning magnification error that occurs individually for each color.

  Various types of image forming processes are known which are employed in an image forming apparatus that forms a color image by electrophotography. One of them is a tandem type image forming apparatus.

  This tandem type image forming apparatus includes an image carrier and an image forming process element for the image carrier for each color to be imaged, and the image carrier and the image forming process element are intermediately transferred. Placed along the body and the paper transport belt, the images formed for each color are superimposed on the intermediate transfer body, and the superimposed full color image is transferred onto the paper at a time or transported by the paper transport belt Each time a sheet passes through the transfer process of each image carrier, a color image formed on each image carrier is transferred onto a recording medium and passed through all transfer stations to form a full color image. Is. The configuration of the tandem type color image forming apparatus will be described below with reference to FIG. Note that the tandem type color image forming apparatus shown in FIG. 1 is an image forming apparatus that sequentially transfers an image formed for each color onto a transfer sheet.

  The image forming apparatus shown in FIG. 1 has image forming units (100Y, 100M, 100C, 100K) that form images of different colors (yellow: Y, magenta: M, cyan: C, black: K) on transfer paper. It is arranged in a line on the upstream side in the transport direction along the transport belt (2) for transporting (1).

  The conveying belt (2) is stretched between a driving roller (3) that is driven and rotated on one side and a conveying roller (4) that is a driven roller that is driven and rotated on the other side. 3), the rotation is driven in the direction of the arrow shown in FIG. 1 (counterclockwise in FIG. 1).

  In addition, a paper feed tray (5) in which transfer paper (1) is stored is provided below the transport belt (2). The transfer paper at the uppermost position among the transfer paper (1) stored in the paper feed tray (5) is fed at the time of image formation and is sucked onto the transport belt (2) by electrostatic suction. Then, the transfer paper (1) adsorbed on the conveyance belt (2) is conveyed to the first image forming unit (100Y), and the yellow image formed by the first image forming unit (100Y) is transferred. It is transferred onto the transfer paper (1).

  The first image forming unit (100Y) includes a photosensitive drum (6Y), a charger (7Y) disposed around the photosensitive drum (6Y), an exposure unit (8), a developing unit (9Y), a photosensitive unit. It is composed of a body cleaner (10Y).

  The surface of the photosensitive drum (6Y) is uniformly charged by a charger (7Y), and then exposed by a laser beam (11Y) corresponding to a yellow image by an exposure device (8), whereby an electrostatic latent image is formed. It is formed on the photosensitive drum (6Y). The electrostatic latent image formed on the photosensitive drum (6Y) is developed by the developing unit (9Y), and a toner image is formed on the photosensitive drum (6Y). This toner image is transferred onto the transfer paper (1) by the transfer device (12Y) at a position (transfer position) where the photosensitive drum (6Y) contacts the transfer paper (1) on the transport belt (2). 1) A monochromatic (yellow) image is formed on top. After the transfer, the photosensitive drum (6Y) is cleaned with unnecessary toner remaining on the surface of the photosensitive drum (6Y) by the photosensitive cleaner (10Y) to prepare for the next image formation.

  The transfer paper (1) having the single color (yellow) transferred by the first image forming unit (100Y) in this way is transported to the second image forming unit (100M) by the transport belt (2). In this case as well, the toner image (magenta) formed on the photosensitive drum (6M) is similarly transferred onto the transfer paper (1). The transfer paper (1) is further conveyed sequentially to the third image forming unit (100C) and the fourth image forming unit (100K), and similarly formed (cyan, black) toner images are transferred to the conveying belt. The images are sequentially transferred onto the transfer paper (1) conveyed by (2), and a color image is formed on the transfer paper (1). In the image forming apparatus shown in FIG. 1, the toner image formed by each image forming unit (100Y, M, C, K) is transferred onto the transfer paper (1) that has been transported by the transport belt (2). The scanning timing of each color laser beam, the sub-scanning timing of the photosensitive drum, and the conveyance speed of the conveyance belt are controlled so as to match.

  By the above control, the transfer paper (1) on which the color image is formed by passing through the fourth image forming unit (100K) is peeled off from the conveying belt (2) and fixed by the fixing device (13). Then, the paper is discharged.

Next, the configuration of the exposure device (8) shown in FIG. 1 will be described with reference to FIG.
FIG. 2 is a schematic plan view of the optical unit constituting the exposure device (8) shown in FIG. 1 as viewed from above.

  In the optical unit constituting the exposure device (8) shown in FIG. 1, the light beams from the LD unit BK (16) and the LD unit Y (17) pass through the cylinder lenses CYL_BK (18) and CYL_Y (19) and are reflected. The light is incident on the lower surface of the polygon mirror (22) by the mirror BK (20) and the reflection mirror Y (21), and the polygon mirror (22) rotates to deflect the light beam, and the fθ lens BKC (23) and The light passes through the fθ lens MY (24) and is folded by the first mirror BK (25) and the first mirror Y (26).

  On the other hand, the light beams from the LD unit C (27) and the LD unit M (28) pass through the CYL_C (29) and CYL_M (30), enter the upper surface of the polygon mirror (22), and enter the polygon mirror (22 ) Rotates to deflect the light beam, pass through the fθ lens BKC (23) and the fθ lens MY (24), and are folded back by the first mirror C (31) and the first mirror M (32).

  Further, upstream of the writing position in the main scanning direction, cylinder mirrors CYM_BKC (33) and CYM_MY (34), a synchronization sensor 1BKC (35), and a synchronization sensor 1MY (36) are provided, and an fθ lens BKC (23). And the fθ lens MY (24) are reflected and collected by the CMY_BKC (33) and the CYM_MY (34), and enter the synchronous sensor 1BKC (35) and the synchronous sensor 1MY (36). Yes. The synchronization sensor 1BKC (35) and the synchronization sensor 1MY (36) are synchronization detection sensors for synchronizing in the main scanning direction.

  Further, similarly to the upstream side, the cylinder mirrors CMY_BKC (37) and CYM_MY (38), the synchronization sensor 2BKC (39), and the synchronization sensor 2MY (40) are provided downstream of the image area in the main scanning direction, and fθ The light beam that has passed through the lens KC (23) and the fθ lens MY (24) is reflected and collected by the CMY_BKC (37) and CYM_MY (38), and enters the synchronous sensor 2BKC (39) and the synchronous sensor 2MY (40). It has a configuration like this.

  Further, in the light beams from the LD unit BK (16) and the LD unit C (27), the common CMY_BKC (33) and the synchronous sensor 1BKC (35) on the write start side, and the common CMY_BKC (37) and the write end side The synchronous sensor 2BKC (39) is used. The same applies to the LD unit Y (17) and the LD unit M (28).

  In the scanning optical system shown in FIG. 2, since two color light beams are incident on the same sensor, by making the incident angles of the light beams of the respective colors different from each other on the polygon mirror (22), The timing at which the light beam enters each sensor can be changed, and the light beam is output as a pulse train in time series.

  In the scanning optical system shown in FIG. 2, since the fθ lens (23, 24) is configured to be independent of color, due to factors such as manufacturing variations and mounting variations of the fθ lens (23, 24), The scanning magnification on the photosensitive drum of each color has an error different from the optical ideal magnification. In the scanning optical system shown in FIG. 2, an fθ lens (23, 24) is used for one-dimensional scanning of each color laser beam deflected and scanned by one polygon mirror (22) onto the photosensitive drum of each color. The laser beam after passing is reflected by the first mirror (25, 26, 31, 32).

  Further, the scanning directions of the laser light on the photosensitive drum using the facing surface of the polygon mirror (22) are respectively opposite to each other. For example, in the scanning optical system shown in FIG. 2, when K and C laser beams scan the photosensitive drum in the forward direction, M and Y laser beams scan the photosensitive drum in the reverse direction. Will do.

  Further, in the configuration of the scanning optical system shown in FIG. 2, in the case of forming an image of a plurality of colors, the laser beams for one-dimensional scanning of the laser beams of each color are independently modulated and controlled. .

  The laser light of each color is timed based on a reference signal (DETECT signal) from a synchronous sensor (35, 36, 39, 40) that detects a reference position in the main scanning direction of the rotational scanning position by the polygon mirror (22). Be controlled.

  In the case of the configuration of the scanning optical system shown in FIG. 2, the scanning magnification of each color passes through a separate scanning optical system, so that each has a slightly different scanning magnification error. Therefore, in order to correct the scanning magnification error, for example, as shown in FIG. 3, the PLL circuit (100) is provided independently for each color (Bk, C, Y, M), and the difference in scanning magnification error is determined. Absorbed. The circuit configuration shown in FIG. 3 will be described below. The circuit configuration shown in FIG. 3 shows the configuration of a clock circuit that scans laser light of each color and generates a laser modulation clock for modulating the laser light in accordance with image data.

  The clock circuit shown in FIG. 3 includes a PLL (phase locked loop) unit (100), a frequency divider (101), and a periodic modulator (102) for each color (Bk, C, Y, M). And have a configuration.

  The PLL unit (100) generates a high frequency clock corresponding to the set value from the reference clock, and outputs the generated high frequency clock to the frequency divider (101). The frequency divider (101) divides the high-frequency clock, and outputs the frequency-divided clock to the period modulator (102). The frequency modulator (102) generates a laser modulation clock for each color based on the divided clock and the period modulation signal for each color.

  As described above, the conventional clock circuit that scans the laser light of each color and generates the laser modulation clock for modulating the laser light according to the image data has the PLL circuit (100) independent for each color. The scanning magnification error with respect to the ideal scanning magnification of the scanning optical system shown in FIG.

In addition, as a technical document filed prior to the present invention, it has a modulation unit that modulates each of the light beams generated from each of a plurality of light sources by an image signal, and a clock generation unit that generates a clock of the image signal, In an image forming apparatus that forms an image on a photoconductor by irradiating the photoconductor with a plurality of light beams via a common scanner optical system, the main beam on the photoconductor due to a difference or variation in the wavelength of the light beam. A magnification color compensation means for compensating for a shift in the imaging position in the scanning direction is provided in the scanner optical system, and at least two of the clocks of the plurality of image signals for modulating each of the plurality of light beams. By using a clock in common, it is possible to form a good image with low-cost and high-accuracy imaging of the light beams generated from the difference in wavelength and each of the plurality of light sources. There is an image forming apparatus to be (for example, see Patent Document 1).
JP 2000-212431 A

  As shown in FIG. 3, the conventional clock circuit for generating the laser modulation clock has a PLL section (100) for each color, which causes an increase in cost. Currently. Similarly, Patent Document 1 is also configured with a plurality of PLL units, which causes an increase in cost.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image forming apparatus that uses a common high-frequency clock for each color to reduce costs.

  In order to achieve this object, the present invention has the following features.

An image forming apparatus according to the present invention includes :
An image forming apparatus that scans light on an image carrier and forms an image of each color on the image carrier,
High-frequency clock generation means shared by at least two colors for generating a high-frequency clock corresponding to a set value from a reference clock;
Dividing means for dividing the high-frequency clock and generating the divided clock,
Based on the frequency-divided clock, periodic modulation means for generating a modulation clock for modulating light of each color in the main scanning direction;
Selecting means for selecting the high-frequency clock generating means,
The period modulation unit corrects a scanning magnification error different for each color independently for each color,
The selection means selects the high-frequency clock generation means that minimizes the number of corrections independently for each color, and outputs the high-frequency clock generated by the selected high-frequency clock generation means to the frequency division means It is characterized by doing.

According to the present invention , it is possible to reduce the cost by using a common high-frequency clock for each color.

  First, the features of the image forming apparatus according to the present embodiment will be described with reference to FIG.

  The image forming apparatus according to the present embodiment is an image forming apparatus that scans light on an image carrier and forms an image of each color on the image carrier, as shown in FIG. 4, from a reference clock to a set value. High-frequency clock generation means (100) for generating a corresponding high-frequency clock, and modulation clock generation means (101, 102) for dividing the generated high-frequency clock and generating a modulation clock for modulating light of each color in the main scanning direction The high frequency clock generating means (100) is shared by at least two colors, and the number of high frequency clock generating means (100) is smaller than the number of colors forming an image on the image carrier. Is. This makes it possible to reduce the cost by using a common high-frequency clock for each color. Hereinafter, an image forming apparatus according to the present invention will be described with reference to the accompanying drawings.

(First embodiment)
First, a laser modulation clock generation circuit mounted on the image forming apparatus of this embodiment will be described with reference to FIG. FIG. 4 shows a configuration of a clock circuit that scans laser light of each color and generates a laser modulation clock for modulating the laser light in accordance with image data.

  As shown in FIG. 4, the laser modulation clock generation circuit mounted on the image forming apparatus according to the present embodiment includes two PLL (phase locked loop) units (100) and a frequency divider provided for each color. (101) and a periodic modulator (102).

  The PLL unit (100) generates a high frequency clock corresponding to the set value from the reference clock, and outputs the generated high frequency clock to the frequency divider (101). The frequency divider (101) divides the high-frequency clock, and outputs the frequency-divided clock to the period modulator (102). The frequency modulator (102) generates a laser modulation clock for each color based on the divided clock and the period modulation signal for each color.

  As described above, the laser modulation clock generation circuit mounted on the image forming apparatus according to the present embodiment has two PLL units (100), and the PLL unit (100 for Bk color and C color, Y color and M color). ) Can be made smaller than the conventional circuit configuration shown in FIG.

  When the PLL unit (100) is shared by each color, it becomes necessary to absorb the difference in scanning magnification error of each color. For this reason, the image forming apparatus according to the present embodiment uses a scanning modulator error as an ideal magnification within a range that does not affect the actual image in the periodic modulator (102) that increases or decreases the period of the laser modulation clock. The scanning magnification error is corrected so as to approach the error, and the difference in the scanning magnification error of each color is absorbed.

  The periodic modulation process in the periodic modulator (102) is performed multiple times at an arbitrary position in the main scanning direction, and the scanning magnification error is corrected so that the scanning magnification over the entire length in the main scanning direction approaches the ideal magnification. Will do. Hereinafter, the period modulation processing of the laser modulation clock in the period modulator (102) will be described with reference to FIG.

  As shown in FIG. 5, the periodic modulator (102) has a minute time α (for example, T / 8) with respect to the normal clock period T at the timing (at the time of rising) when the periodic modulation signal is input. > Α) is added to the clock cycle of T + α. By performing this periodic modulation process a plurality of times at an arbitrary position in the main scanning direction, it is possible to accurately bring a minute scanning magnification error close to the ideal scanning magnification.

  Based on the laser modulation clock on which the periodic modulation processing shown in FIG. 5 is performed, the laser light is one-dimensionally scanned to form an image close to the ideal scanning magnification on the photosensitive drum of each color. It is possible to reduce the amount of color misregistration in the case of overlapping.

  In FIG. 5, the period modulator (102) modulates the clock period when the period modulation signal rises. However, the period modulator (102) modulates the clock period when the period modulation signal falls. Is also possible.

  In FIG. 5, the periodic modulator (102) modulates to a clock cycle of T + α by adding a minute time α (for example, T / 8> α) at the timing (at the time of rising) when the periodic modulation signal is input. However, as shown in FIG. 6, at the timing when the period modulation signal is input (at the time of rising), modulation is performed to a T-α clock period obtained by subtracting a minute time α (for example, T / 8> α). Sometimes it does.

  As described above, the image forming apparatus according to the present embodiment controls the period modulator (102) that lengthens or shortens the period of the laser modulation clock a plurality of times at an arbitrary position in the main scanning direction. Even in a color in which the part (100) is shared, each color can be controlled independently.

  In the image forming apparatus described above, the control processing in the case of a circuit configuration having two PLL units (100) as shown in FIG. 4 has been described. However, as shown in FIG. On the other hand, it is also possible to construct a circuit configuration having one PLL unit (100) or a circuit configuration having three PLL units (100) as shown in FIG. For this reason, according to the configuration of the image forming apparatus, the circuit configuration having the optimum number of PLL units (100) is appropriately selected from the circuit configurations shown in FIGS. Will be installed.

  The above-described periodic modulation processing shown in FIG. 5 and FIG. 6 causes the actual image to extend and contract even though it is very small. Therefore, depending on the degree of influence on the image, the PLL unit (100 shared by each color) ) And which color should be shared.

(Second Embodiment)
Next, a second embodiment will be described.

  As shown in FIGS. 9 and 10, the image forming apparatus according to the second embodiment includes a PLL selection unit (200) that selects the PLL unit (100). The PLL selection unit (200) is discrete. The PLL unit (100) is selected so that the number of corrections for independently correcting different scanning magnification errors for each color caused by an arbitrary frequency for each color is minimized in the periodic modulator (102). It is characterized by. This makes it possible to form a higher quality image. Hereinafter, the image forming apparatus according to the second embodiment will be described with reference to FIGS. 9 and 10.

  As shown in FIGS. 9 and 10, the laser modulation clock generation circuit mounted on the image forming apparatus in the second embodiment minimizes the influence on the image by the period modulation processing in the period modulator (102). Therefore, based on the measurement information of the scanning magnification error of each color shared by the PLL unit (100), a setting value is set so that the number of period modulation processes in one period of each color is minimized. The selected PLL unit (100) is selected, and the high-frequency clock generated by the selected PLL unit (100) is output to the frequency divider (101).

  The scanning magnification error of the scanning optical system corresponding to each color is considered to vary among image forming apparatuses, but the laser modulation clock generation circuit shown in FIGS. 4, 7, and 8 is shared by each color. There are cases where the PLL unit (100) is fixed and the influence on the image due to the periodic modulation processing cannot be minimized.

  For this reason, as shown in FIGS. 9 and 10, the image forming apparatus according to the present embodiment is newly provided with a PLL selection unit (200) that selects a PLL unit (100) that outputs an arbitrary high-frequency clock. Even when the scanning magnification error characteristic differs for each image forming apparatus, the PLL unit (100) selected by the PLL selection unit (200) can be shared by scanning optical systems having colors as close as possible to the scanning magnification error characteristic. It becomes possible. Thereby, it is possible to minimize the period modulation processing of each color and form an image with less influence by the period modulation processing.

(Third embodiment)
Next, a third embodiment will be described.

  The image forming apparatus according to the third embodiment has a polygon mirror having a plurality of light deflection surfaces for deflecting and scanning laser light, and the polygon mirror is shared by at least two colors, and an image is formed on the photosensitive drum. In an image forming apparatus configured with fewer numbers than colors to be formed, the PLL unit (100) is shared by a color in which laser light is simultaneously deflected and scanned using the same light deflection surface. It is. As a result, the number of periodic modulation processes for each color performed in the periodic modulator (102) can be reduced, and a high-quality image can be formed in which the influence of the periodic modulation process is reduced. The image forming apparatus according to the third embodiment will be described below.

  In the case of the scanning optical system shown in FIG. 2, the image forming colors corresponding to the laser beams that are always deflected and scanned by the same optical deflection surface among the optical deflection surfaces of the polygon mirror (22) are (Bk color, C color), This is a combination of (Y color, M color), and it is assumed that the scanning magnification error characteristic shows a characteristic close to the combination. For this reason, the image forming apparatus according to the third embodiment has the PLL unit (100) in the image forming color corresponding to the light that is always deflected and scanned by the same optical deflection surface among the optical deflection surfaces of the polygon mirror (22). By sharing, it is possible to reduce the number of times of periodic modulation processing of each color performed in the periodic modulator (102), and to form a high-quality image that is less affected by the periodic modulation processing.

(Fourth embodiment)
Next, a fourth embodiment will be described.

  In the image forming apparatus according to the fourth embodiment, a PLL unit (100) is preferentially assigned to a color that appears to be affected by a scanning magnification error, and the assigned PLL unit (100) is shared with other colors, thereby generating a high frequency signal. The setting value for generating the clock is set in accordance with the characteristics of the scanning optical system of the color in which the influence of the scanning magnification error appears. As a result, the number of periodic modulation processes for each color performed in the periodic modulator (102) can be reduced, and a high-quality image can be formed in which the influence of the periodic modulation process is reduced. The image forming apparatus according to the fourth embodiment will be described below.

  In the actual image, the influence on the final formed image due to the scanning magnification error is largely influenced by the sensitivity of human appearance, and the influence of the color misregistration amount due to the slight scanning magnification error is easy to visually recognize the final formed image. There are colors and colors that are difficult to see. For this reason, the image forming apparatus according to the fourth embodiment considers the difference in the degree of influence on the final formed image, and for example, the degree of influence on the final formed image is C color> M color> Bk color> Y color. If the order is different, the color combination for sharing the PLL unit (100) is (C color, Bk color), (M color, Y color), and the set frequency in the PLL unit (100) is more Image forming color having a large influence: By setting according to the magnification error characteristic of the scanning optical system corresponding to C color and M color, control is performed so that periodic modulation processing for C color and M color is minimized. Therefore, it is possible to form a high-quality image that is less affected by the periodic modulation process.

(Fifth embodiment)
Next, a fifth embodiment will be described.

  The image forming apparatus according to the fifth embodiment measures a scanning time during which light of each color scans in the main scanning direction, and in the periodic modulator (102), an ideal that is different for each color according to the measured scanning time. The amount of deviation with respect to a proper scanning magnification is corrected so that each becomes an appropriate scanning magnification. Thereby, it is possible to form an image in which the scanning magnification error of each color is reduced.

  Conventionally, correction data for correcting a magnification error has been obtained by measuring each scanning magnification error of the scanning optical system for each image forming apparatus. However, depending on the installation status and operating state of the image forming apparatus, image formation is performed. It is assumed that the environmental temperature inside the apparatus fluctuates. For this reason, as the environmental temperature in the image forming apparatus changes, the optical characteristics of the scanning optical system mounted in the image forming apparatus change, and the scanning magnification of the scanning optical system also changes. Conventionally, a detector for detecting fluctuations in scanning magnification is provided in the image forming apparatus, the scanning magnification is measured at a predetermined timing using the provided detector, and scanning is performed according to the measured result. Magnification correction was performed. On the other hand, the image forming apparatus according to the fifth embodiment is an image forming apparatus in which the PLL unit (100) is shared by at least two colors and the PLL units (100) are configured with a smaller number than the image forming colors. The scanning time for each color of light to scan in the main scanning direction is measured, and in accordance with the measured scanning time, the period modulator (102) has an appropriate amount of deviation with respect to an ideal scanning magnification different for each color. By correcting the scanning magnification error so as to achieve the scanning magnification, an image in which the scanning magnification error of each color is always reduced is formed regardless of the installation state and operation state of the image forming apparatus.

  As shown in FIG. 2, the image forming apparatus according to the fifth embodiment includes a photodetector (35, 36) for detecting the front end position of the laser beam in the main scanning direction and the rear end of the laser beam in the main scanning direction. And a photodetector (39, 40) for detecting the position, a photodetector (35, 36) for detecting the laser beam on the front end side, and a photodetector (39 for detecting the laser beam on the rear end side). , 40), and the difference in the laser beam passage timing from the leading end position to the trailing end position is measured, and the scanning time for scanning each color laser beam in the main scanning direction is measured. It will be. Then, the PLL frequency and the number of times of periodic modulation processing for each color are determined according to the measured scanning time of each color laser beam, and magnification error correction is performed. As a result, it is possible to form a high-quality color image with little scanning magnification error and color misregistration. Note that the magnification error correction described above can be configured to be performed at an arbitrary timing regardless of the operating state of the image forming apparatus, changes in environmental temperature, and the like.

(Sixth embodiment)
Next, a sixth embodiment will be described.

  As shown in FIGS. 11 and 12, an image forming apparatus according to the sixth embodiment includes an image carrier (3) and image processing means (4, 4) used when an image is formed on the image carrier (3). In the image forming apparatus having the process cartridge (1) which is integrated with the plurality of subunits 5 and 6) and detachable from the main body of the image forming apparatus, the same magnification error correction as that of the image forming apparatus described above is performed. It is a feature. The image forming apparatus according to the sixth embodiment will be described below with reference to FIGS. 11 and 12. Note that the image process means in the image forming apparatus of the present embodiment is composed of at least one of the developing device (5), the cleaning device (6), and the charging device (4).

  First, the configuration of the process cartridge (1) mounted in the image forming apparatus of the present embodiment will be described with reference to FIGS.

  As shown in FIGS. 11 and 12, the process cartridge (1) in this embodiment includes a process cartridge frame (2a, 2b), a photosensitive drum (3) as a latent image carrier, and each process means. A charging module (4) that is a charging device to be constructed, a developing module (5) that is a developing device, and a cleaning module (6) that is a cleaning device are configured.

  In this embodiment, the process cartridge (1) is replaced with a new one for the photosensitive drum (3), the charging module (4), the developing module (5), and the cleaning module (6). It is built to be possible.

  The process cartridge frame (2a, 2b) has an open position in which the first process cartridge frame (2a) and the second process cartridge frame (2b) are centered on the engaging portion (2c). And a closed position are rotatably engaged. In the closed position, the first process cartridge frame (2a) and the second process cartridge frame (2b) are arranged so that the photosensitive drum (3) cannot be removed. It is built to surround.

  The engaging portion (2c) is provided with a protrusion and a hole in the first process cartridge frame (2a) and the second process cartridge frame (2b), and the protrusion is inserted into the hole. It is constructed so that it can be engaged and held on the protrusion with a C-ring. Furthermore, in the closed position, the frame body position with respect to the hole provided in the place where the first process cartridge frame (2a) and the second process cartridge frame (2b) overlap. The first process cartridge frame (2a) or the second process cartridge frame (2b) is positioned and fixed by penetrating with two pins planted in a fixing member (not shown). Will do. Thus, the process cartridge can be easily separated by assembling the process cartridge without integrally forming the first process cartridge frame (2a) and the second process cartridge frame (2b). It is possible to construct the photosensitive drum (3), the charging module (4), the developing module (5), and the cleaning module (6) so that the units can be individually replaced.

  Further, the process cartridge (1) in the present embodiment can be configured to be provided with various detection means. As shown in FIG. 12, the temperature and humidity in the process cartridge (1) are detected as the detection means. Temperature / humidity sensor (21) for detecting the potential, a potential sensor (22) for detecting the potential of the photosensitive drum (3), and a toner concentration for detecting the amount of toner developed on the photosensitive drum (3) after development. It is also possible to arrange a sensor (23).

  The temperature / humidity sensor (21) is disposed on the second process cartridge frame (2b) and has a positive temperature characteristic, for example, platinum, tungsten, nichrome, Kanthal, or a negative humidity characteristic, for example, Sic. It is detected by a detection element such as a fine wire such as (carbonized diatom) or TaN (tantalum nitride) or a minute temperature sensitive element such as a thin film or thermistor. In addition, although the temperature / humidity sensor (21) in this embodiment was arrange | positioned in the upper part of the 2nd frame (2b) as shown in FIG. 12, it is not limited to this position and various changes are made. It is possible to arrange them.

  The potential sensor (22) is disposed on the second process cartridge frame (2b), and includes a potential detection unit and a control unit. The potential sensor (22) can detect the surface potential of the photosensitive drum (3) by being arranged at a distance of 1 to 3 mm from the surface of the photosensitive drum (3) of the object to be measured. It is. In addition, as shown in FIG. 12, the electric potential sensor (22) in this embodiment is an upper part of the first process cartridge frame (2a), the charging module (4), and the developing module (5). It is arranged so as to be on the downstream side of the laser beam to be exposed. At this position, the potential of the photosensitive drum (3) on which a latent image that becomes a patch-like solid black portion is formed is detected, and the detected signal is transmitted to the image forming apparatus main body through a signal line. The control unit provided in the apparatus main body determines the magnitude of the developing bias applied by the developing module (5), and controls the power supply to apply the voltage. This potential sensor (22) can also be constructed to detect the potential of the photosensitive drum (3) as the white background portion and control the light amount and exposure time of the laser beam forming the solid black portion. It is.

  The toner density sensor (23) is arranged on the first process cartridge frame (2a), and visualizes the latent image of the solid black portion formed outside the image forming area on the photosensitive drum (3) with toner. The toner adhesion amount of the solid black portion is optically detected as an image density, and the detection result is transmitted as a signal to a control unit included in the image forming apparatus main body. The toner density sensor (23) is composed of a light emitting element (for example, LED) and a light receiving element, and the light receiving element receives the light amount of the light emitting element reflected from the solid black portion, and is on the photosensitive drum (3). The amount of toner is detected. The toner density sensor (23) detects the amount of toner on the photosensitive drum (3), and is accommodated in the developing module (5) from the table recorded in the control unit provided in the main body of the image forming apparatus. The toner density of the developing developer is determined. The toner density sensor (23) in the present embodiment is provided on the downstream side in the developing module (5).

  The various sensors related to the photosensitive drum (3) are arranged in the process cartridge frame (2a, 2b), so that the process means can be easily replaced. In addition, it is possible to reduce the cost of each replaceable process means.

  In addition, as shown in FIG. 12, the process cartridge (1) in the present embodiment can be provided with a pre-transfer neutralization device (25) and a pre-cleaning neutralization device (26). The pre-transfer static eliminator (25) is provided on the upstream side of the transfer region, and the pre-cleaning static eliminator (26) is provided on the downstream side of the transfer region and upstream of the cleaning device, and charges on the photosensitive drum (3) are transferred. By causing the light to decay, transfer or cleaning becomes easy. In particular, the pre-cleaning static eliminator (26) facilitates cleaning of residual toner that has not been transferred onto the photosensitive drum (3). Note that the pre-transfer static eliminator (25) and the pre-cleaning static eliminator (26) are provided with light emitting diodes (LD), LEDs, electroluminescence (EL), fluorescent lamps, etc. as issuing means. In this case, the photosensitive drum (3) is exposed to extinguish charges on the photosensitive drum (3). The issuing means is preferably EL or LD. Furthermore, the structure is simple and it is more preferable to use EL. It is also possible to provide a pre-charge neutralization device upstream of the charging device. Thereby, the residual potential of the photosensitive drum (3) can be erased, and the photosensitive drum (3) can be uniformly charged.

  The process cartridge (1) in the present embodiment is obtained by removing any subunit of the photosensitive drum (3), the charging module (4), the developing module (5), and the cleaning module (6). It is configured so that it can be separated and replaced. In particular, the charging module (4), the developing module (5), and the cleaning module (6) are all constructed so that they can be detached and attached independently of other modules. ing.

  Since the process cartridge (1) in the present embodiment improves the ease of installation operation with the image forming apparatus main body, it may be difficult to accurately attach the photosensitive drum (3). is there.

  In this case, the scanning position of the laser light applied to the photosensitive drum (3) also deteriorates in accuracy, and there is a concern that a scanning magnification error may occur.

  Conventionally, a photodetector for measuring the scanning time has been arranged at a position equivalent to the surface of the photosensitive drum (3) on the image forming apparatus main body side. In this case, the detection result by the photodetector and the actual scanning magnification of the photosensitive drum (3) include an error due to a defective mounting of the process cartridge (1).

  In order to accurately measure the scanning magnification, a photodetector may be arranged on the surface of the photosensitive drum (3) of the process cartridge (1). However, the photodetector on the main scanning front end side is not affected by the mounting failure of the process cartridge (1), and it is necessary to accurately detect the absolute position of the image forming apparatus. This is to determine a reference for correcting the formed image position with respect to the paper transport position.

  Therefore, in the image forming apparatus according to the present embodiment, as shown in FIG. 13, only the photodetector on the rear end side of the main scanning is arranged on the same surface as the photosensitive drum (3) on the process cartridge (1) side. To. Thereby, the main scanning front end side is performed by the photodetector arranged at the main scanning front end position of the scanning optical system that detects the absolute position of the optical scanning position, and the main scanning rear end side is the process cartridge (1) side. By using a photodetector arranged on the same surface as the photosensitive drum (3), it is possible to measure a scanning magnification error in the main scanning direction including an error caused by a mounting failure of the process cartridge (1). It becomes.

  Then, the set frequency of the high-frequency clock generated by the PLL unit (100) and the period modulation by the period modulator (102) according to the measurement result of the scanning magnification error including the attachment error of the photosensitive drum (3) of each color. The number of executions of the process is determined, and a high-quality image in which the scanning magnification error and the color misregistration amount of each color are suppressed is formed.

  If a detection signal cannot be obtained from a photodetector installed on the same surface of the photosensitive drum (3) on the process cartridge (1) side, the photosensitive drum (3) mounted on the process cartridge (1). Is determined to be abnormal, and control is performed to warn that the mounting position of the process cartridge (1) is not normal. Thereby, it becomes possible to warn the outside of the mounting failure of the process cartridge (1). Further, since the photodetector for measuring the scanning magnification also functions as a set detection sensor for warning the mounting failure of the process cartridge (1) to the outside, the mounting failure of the process cartridge (1) is externally provided. Even if a set detection sensor for warning is not provided, it is possible to warn of defective mounting of the process cartridge (1).

  The above-described embodiment is a preferred embodiment of the present invention, and the scope of the present invention is not limited to the above-described embodiment alone, and various modifications are made without departing from the gist of the present invention. Implementation is possible. For example, it is possible to construct the image forming apparatus in the above embodiment by causing the control operation in the image forming apparatus in the above embodiment to be executed as a program in an image forming apparatus such as a copier, a printer, a facsimile, or a complex machine thereof. Is possible.

  The image forming apparatus according to the present invention can be applied to an image forming apparatus such as a copying machine, a printer, and a facsimile.

1 is a diagram illustrating a configuration of a tandem type color image forming apparatus. FIG. It is a figure which shows the structure of the exposure device (8) which the image forming apparatus shown in FIG. 1 comprises. It is a block diagram which shows the structure of the conventional clock circuit which produces | generates a laser modulation clock. It is a block diagram which shows the 1st structural example of the laser modulation clock generation circuit in 1st Embodiment. It is a figure which shows the 1st timing chart for demonstrating the period modulation process of the laser modulation clock in a period modulator (102). It is a figure which shows the 2nd timing chart for demonstrating the period modulation process of the laser modulation clock in a period modulator (102). It is a block diagram which shows the 2nd structural example of the laser modulation clock generation circuit in 1st Embodiment. It is a block diagram which shows the 3rd structural example of the laser modulation clock generation circuit in 1st Embodiment. It is a block diagram which shows the 1st structural example of the laser modulation clock generation circuit in 2nd Embodiment. It is a block diagram which shows the 2nd structural example of the laser modulation clock generation circuit in 2nd Embodiment. FIG. 2 is a diagram illustrating a configuration of a process cartridge mounted on an image forming apparatus according to the present embodiment. FIG. 2 is a schematic cross-sectional view showing a configuration of a process cartridge mounted on the image forming apparatus in the present embodiment. It is a figure which shows a structure at the time of arrange | positioning only the photodetector at the rear end side of the main scanning on the same surface as the photosensitive drum (3) on the process cartridge (1) side.

Explanation of symbols

16 LD unit BK (means for modulating a light beam with an image signal)
17 LD unit Y (means for modulating a light beam with an image signal)
27 LD unit C (means for modulating light beam with image signal)
28 LD unit M (means for modulating a light beam with an image signal)
35 Synchronous sensor 1BKC (front end side light detection means)
36 Synchronous sensor 1MY (front end side light detection means)
39 Synchronous sensor 2BKC (rear end side light detection means)
40 Sync sensor 2MY (rear end side light detection means)
100 PLL section (high frequency clock generating means)
101 frequency divider (modulation clock generation means)
102 period modulator (modulation clock generation means, period modulation means)
200 PLL select section (selection means)

Claims (5)

An image forming apparatus that scans light on an image carrier and forms an image of each color on the image carrier,
High-frequency clock generation means shared by at least two colors for generating a high-frequency clock corresponding to a set value from a reference clock;
The high frequency clock by dividing the frequency dividing means for generating a divided clock frequency dividing,
Based on the frequency- divided clock, periodic modulation means for generating a modulation clock for modulating light of each color in the main scanning direction;
Selecting means for selecting the high-frequency clock generating means,
The period modulation unit corrects a scanning magnification error different for each color independently for each color,
The selection unit selects the high-frequency clock generation unit that minimizes the number of corrections independently for each color, and outputs the high-frequency clock generated by the selected high-frequency clock generation unit to the frequency division unit An image forming apparatus.   2. The image forming apparatus according to claim 1, wherein the high frequency clock generation means is a PLL (Phase Locked Loop) circuit, and generates a discrete arbitrary frequency. The period modulation means includes
3. The image forming apparatus according to claim 2 , wherein a scanning magnification error which is different for each color generated by a discrete arbitrary frequency is corrected independently for each color. The selection means includes
The image forming apparatus according to any one of claims 1 to 3, characterized in that the combination of colors to share the high-frequency clock generating means and can be selected arbitrarily. The selection means includes
5. The image forming apparatus according to claim 4 , wherein the high-frequency clock generating means is shared by colors having similar scanning magnification error characteristics of the respective colors.

Images