JP2013025232A - Image forming apparatus, and control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can reduce the range of light intensity of a laser to be used, and can form images with stable laser characteristics.SOLUTION: In an image forming apparatus, a controller 1027 detects density of toner images formed on the surfaces of photoreceptors 14 to 17 with the use of a density sensor 1010, and calculates target light intensity of a beam from the detection result. If the calculated target light intensity is out of an appropriate range of light intensity, the controller 1027 switches the number of beams of a laser emitted from a LD 100, and switches the rotation speed of a polygon motor for driving and rotating a polygon mirror.

Description

  The present invention relates to an image forming apparatus and a control method thereof, and more particularly to a scanning exposure technique in an electrophotographic image forming apparatus.

  In recent years, in an image forming apparatus using a laser scanning optical system as an exposure unit, a multi-beam laser diode may be used as a light source in order to improve productivity or resolution. For example, when PS: process speed in the vertical direction of laser scanning representing productivity, DPI: resolution, RMS: rotational speed of polygon motor, N: number of polygon surfaces, M: number of beams, the relationship is expressed by the following equation (1). ).

PS = RMS / 60 (25.4 / DPI) (N × M) (1)
According to the above formula, it can be seen that productivity or resolution can be improved by increasing the rotation speed of the polygon motor, the number of polygon surfaces, and the number of beams.

  However, since the rotational speed of the polygon motor has recently approached the limit of 40000 RPM to 50000 RPM, and adverse effects such as temperature rise and noise have become prominent, it is difficult to improve the rotational speed. It is coming. In general, when the mirror surface is increased with the outer diameter being constant, the polygon mirror is a technology that is incompatible with improving the resolution because the optical characteristics are lowered, the spot diameter is enlarged, and the image quality is deteriorated. If the mirror surface is increased with the spot diameter kept constant, the length of one side of the mirror must be kept constant, leading to an increase in the outer diameter of the polygon mirror, causing further problems such as temperature rise and noise. Result.

  On the other hand, a surface emitting laser diode (VCSEL) has recently been studied as an exposure unit of an image forming apparatus, compared to a conventional edge emitter laser diode. Since VCSEL emits laser light from the surface of the wafer, it is possible to two-dimensionally arrange light emitting points with respect to the edge emitter LD that emits laser light from the end surface of the wafer. For this reason, there is an advantage that it can easily cope with an increase in the number of beams.

  For these reasons, VCSELs are promising as light sources for exposure means of image forming apparatuses for improving productivity or resolution.

  Moreover, a wide light amount control range is required for the light source of the exposure means of the electrophotographic apparatus. The amount of light from the laser light source is proportional to the process speed, but inversely proportional to the photoreceptor sensitivity, optical efficiency, and number of beams. The sensitivity of the photoconductor has a sensitivity change characteristic due to variations in manufacturing and durability deterioration. When the sensitivity changes, the density of the formed image may be different even when charged, exposed and developed with the same process amount. Therefore, in order to suppress this density fluctuation, there is a method of controlling the exposure amount according to the change in the photoreceptor sensitivity. For example, in the density adjustment sequence, a predetermined inspection image is exposed on the photoconductor, and the surface potential of the photoconductor and the density of the developed toner image are measured by a sensor or the like, so that the target density is obtained. Control the amount of laser light. At this time, since the light source is required to have a light amount that satisfies the fluctuation range of the sensitivity of the photoconductor, the laser needs to control a wide light amount range.

  The optical system controls the light amount on the chip surface so that the light amount of the spot imaged on the photoconductor satisfies the required specifications. However, in the optical system, there are variations in various factors such as variations due to assembly accuracy, lens and mirror transmittance, variations in reflectance, and variations in laser emission angle (FFP). The relationship between the upper light amount and the laser chip surface light amount also varies. In consideration of this variation, the laser is required to control a wide light amount range. For example, a method is disclosed in which, during setup, the average potential and potential variation of a reference patch having a size corresponding to one round of the potential sensor photoreceptor are obtained, and the laser light quantity is set based on the average potential (see, for example, Patent Document 1). ). The setup time means, for example, when the power is turned on or when there is no job for a predetermined time.

JP 2000-056522 A

  Conventionally, a wide range of light quantity is required by a laser. This is due to variations in FFP, variations in the assembly accuracy of the optical system, variations in the sensitivity of the photoreceptor, deterioration in durability, and the like. At this time, when the same laser diode is used from the high light quantity to the low light quantity, the difference in the delay time of the rise affects the image quality, and it is difficult to make the image quality uniform.

  The present invention has been made in view of the above problems, and provides an image forming apparatus capable of narrowing a light amount range of a laser to be used and forming an image with a certain laser characteristic, and a control method thereof. The purpose is to do.

  In order to achieve the above object, an image forming apparatus of the present invention includes a light source that emits a plurality of beams, a driving unit that rotationally drives a rotary polygon mirror, and a plurality of beams that are emitted from the light source. In an image forming apparatus, comprising: a scanning exposure unit that scans and exposes the surface of a photoconductor by deflecting by a rotationally driven rotary polygon mirror; and a control unit that controls a rotation speed of the driving unit. Detecting means for detecting the state of the image to be detected, and calculating means for calculating the target light amount of the beam from the detection result by the detecting means, wherein the control means is configured such that the calculated target light amount is out of a predetermined range. In this case, the number of the plurality of beams emitted from the light source is switched, and the rotation speed of the driving unit is switched.

  According to the present invention, by determining the number of laser beams according to the light amount of the laser that is the light source, it is possible to narrow the light amount range of the laser to be used. In addition, it is possible to form an image with a certain laser characteristic and to prevent the influence on productivity by switching the polygon motor speed according to the number of laser beams.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to a first embodiment of the present invention. It is a figure which shows schematic structure of the scanning exposure apparatus in FIG. It is a figure which shows the circuit structural example of the laser diode in FIG. 2, and a laser driver. It is a figure which shows the relationship between a photoreceptor sensitivity and the light quantity of each laser, (a) is a case where optical efficiency is low, (b) is a case where optical efficiency is high. 6 is a flowchart showing a flow of processing for determining the number of laser beams in the image forming apparatus. It is a figure which shows the relationship between the beam number of a laser beam, and the rotational speed of a polygon motor. (A) is a sequence diagram of image data at the time of image formation with 16 beams, and (b) is a sequence diagram of image data at the time of image formation with 10 beams. It is a figure which shows the relationship between the FFP of the laser in the 2nd Embodiment of this invention, and the light quantity of the chip surface of each laser.

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

[First Embodiment]
FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus according to the first embodiment of the present invention.

  In FIG. 1, the image forming apparatus includes two cassette sheet feeding units 1 and 2 and one manual sheet feeding unit 3. The transfer paper S is selectively fed from the paper feeding units 1, 2, and 3. The transfer paper S is stacked on the cassettes 4 and 5 or the tray 6 of each paper feed unit, and is fed out in order from the highest one by the pickup roller 7. The transfer sheet S fed out by the pickup roller 7 is separated only by the uppermost transfer sheet by a separation roller pair 8 including a feed roller 8A as a conveying unit and a retard roller 8B as a separating unit, and the rotation is stopped. It is sent to the registration roller pair 12. In this case, the transfer sheet S fed from the cassettes 4 and 5 having a long distance to the registration roller pair 12 is relayed to the plurality of conveyance roller pairs 9, 10 and 11 and sent to the registration roller pair 12.

  The transfer paper S sent to the registration roller pair 12 is temporarily stopped when the leading edge of the transfer paper hits the nip of the registration roller pair 12 to form a predetermined loop. By forming this loop, the skew state of the transfer sheet S is corrected.

  A long intermediate transfer belt (endless belt) 13 that is an intermediate transfer member is stretched around a driving roller 13a, a secondary transfer counter roller 13b, and a tension roller 13c downstream of the registration roller pair 12, and in a cross-sectional view. It is set to be approximately triangular. The intermediate transfer belt 13 rotates in the clockwise direction in the figure. On the upper surface of the horizontal portion of the intermediate transfer belt 13, a plurality of photosensitive members (photosensitive drums) 14, 15, 16, and 17 that form and carry color toner images of different colors are sequentially arranged along the rotation direction of the intermediate transfer belt 13. Has been.

  Note that the photosensitive member 14 located on the most upstream side in the rotation direction of the intermediate transfer belt 13 carries a magenta toner image. The photoconductor 15 located on the downstream side of the photoconductor 14 carries a cyan toner image. The photoconductor 16 located on the downstream side of the photoconductor 15 carries a yellow toner image. The photoreceptor 17 located on the most downstream side carries a black toner image.

  First, the exposure of the laser beam LM based on the image of the magenta component is started on the photoreceptor 14 positioned on the most upstream side, and an electrostatic latent image is formed on the photoreceptor 14. This electrostatic latent image is visualized by magenta toner supplied from the developing unit 23.

  Next, exposure of the laser beam LC based on the cyan component image is started on the photoconductor 15, and an electrostatic latent image is formed on the photoconductor 16. This electrostatic latent image is visualized by cyan toner supplied from the developing device 24.

  Next, after a predetermined time has elapsed from the start of exposure of the laser beam LC on the photoconductor 15, exposure of the laser beam LY based on the yellow component image is started on the photoconductor 16, and an electrostatic latent image is formed on the photoconductor 16. It is formed. This electrostatic latent image is visualized by yellow toner supplied from the developing device 25.

  Next, after a predetermined time has elapsed from the start of exposure of the laser beam LY onto the photoconductor 16, exposure of the laser beam LB based on the black component image is started on the photoconductor 17, and an electrostatic latent image is formed on the photoconductor 17. Is formed. The electrostatic latent image is visualized by black toner supplied from the developing device 26.

  In addition, primary chargers 27, 28, 29, and 30 are installed around the photoconductors 14 to 17 to uniformly charge the photoconductors 14 to 17, respectively. In addition, cleaners 31, 32, 33, and 34 for removing toner adhering to the photoconductors 14 to 17 after the toner image is transferred are also installed.

  In the process of rotating the intermediate transfer belt 13 clockwise, a magenta toner image is transferred onto the intermediate transfer belt 13 by passing through a transfer portion between the photoreceptor 14 and the transfer charger 90. Next, a cyan toner image is transferred onto the intermediate transfer belt 13 by passing through a transfer portion between the photoconductor 15 and the transfer charger 91. Next, the yellow toner image is transferred onto the intermediate transfer belt 13 by passing through a transfer portion between the photoconductor 16 and the transfer charger 92. Finally, a black toner image is transferred onto the intermediate transfer belt 13 by passing through a transfer portion between the photoconductor 17 and the transfer charger 93. As described above, magenta, cyan, yellow, and black toner images are transferred onto the intermediate transfer belt 13 in an overlapping manner. On the other hand, the transfer sheet S is sent to the registration roller pair 12 to correct the skew state.

  The registration roller pair 12 starts to rotate at the timing of aligning the position of the toner image on the intermediate transfer belt 13 and the leading edge of the transfer paper.

  Next, the transfer sheet S is sent by the registration roller pair 12 to the secondary transfer portion T2 which is a contact portion between the secondary transfer roller 40 and the secondary transfer counter roller 13b on the intermediate transfer belt 13, and on the sheet surface. The toner image is transferred to the surface. The transfer sheet S that has passed through the secondary transfer portion T2 is sent by the intermediate transfer belt 13 to a fixing device 35 that is an image fixing unit. Then, in the process in which the transfer sheet S passes through the nip formed by the fixing roller 35A and the pressure roller 35B in the fixing device 35, the transfer paper S is heated by the fixing roller 35A and pressurized by the pressure roller 35B to be transferred toner. The image is fixed on the sheet surface. The fixing-processed transfer sheet S that has passed through the fixing device 35 is sent to the discharge roller pair 37 by the conveying roller pair 36 and further discharged onto the discharge tray 38 outside the apparatus.

  In this image forming apparatus, double-sided mode image formation is possible. Hereinafter, the configuration of the image forming apparatus will be further described along the flow of the transfer sheet S in the duplex mode.

  When the duplex mode is designated, the transfer-processed transfer sheet S that has passed through the fixing device 35 is sent to the reverse path 59 through the vertical path 58. In this case, the flapper 60 is open to the vertical path 58 side, and the transfer sheet S that has been subjected to the fixing process is transported by the transport roller pairs 36, 61, 62 and the reverse roller pair 63. When the rear end of the fixed transfer sheet S conveyed in the direction of arrow a by the reverse roller pair 63 passes the point P, the reverse roller pair 63 reverses, and the fixed transfer sheet S moves on the rear end side. It is conveyed in the direction of arrow b starting from the top. With this operation, the toner image transfer surface of the transfer sheet S that has been subjected to the fixing process is on the upper side.

  At the point P, a flapper 64 with flexible transfer paper that allows the transfer paper S to enter from the vertical path 58 to the reversal path 59 and that the transfer paper S cannot enter, and a rear end of the transfer paper Is provided with a detection lever 65 for detecting that the vehicle has passed the point P.

  The fixed sheet S conveyed in the direction of the arrow b by the reverse rotation of the reverse rotation roller pair 63 is sent into the refeed path 67 and relayed by a plurality of refeed path conveyance rollers 68 and the conveyance roller pair 11. The image is again sent to the registration roller pair 12 for image formation. The transfer sheet S that has been subjected to the fixing process is corrected in the skew state by the registration roller pair 12 and then sent to the secondary transfer portion T2. Then, the second image formation is performed based on the image data stored in the image memory (not shown) that has been subjected to magnification correction in the main scanning direction and the sub-scanning direction. Thereafter, the same process as the one-sided image formation is performed. Then it is discharged out of the machine.

  In recent years, in order to increase the speed and image quality of printers and copiers, multiple scanning exposures can be performed by a single scanning operation using a rotating polygon mirror (polygon mirror) with a plurality of semiconductor laser beams used as a light source. Many have been taken. In particular, edge emitting lasers have been put to practical use as surface emitting lasers, and it has become easier to increase the number of beams.

  Next, an example in which a multi-beam semiconductor laser is used in an image forming apparatus will be described below.

  FIG. 2 is a diagram showing a schematic configuration of the scanning exposure apparatus in FIG.

  As shown in FIG. 2, the electrophotographic image forming apparatus is an exposure unit that irradiates the photoconductor 15 with laser light so as to form a latent image corresponding to the input image data on the photoconductor 15. Is provided. This exposure unit includes an LD 100 as a light source for emitting laser light (beam). Laser light emitted from the LD 100 is converted into parallel laser light L1 via a collimator lens 1013, and this L1 is irradiated to a polygon mirror 1002 that is being rotationally driven by a polygon motor 1003. Then, L1 irradiated to the polygon mirror 1002 is deflected by the polygon mirror 1002 and reaches the f-θ lens 1014.

  Further, the polygon motor 1003 is driven at a predetermined rotational speed by a control signal from the controller 1027. The laser beam that has passed through the f-θ lens 1014 is combined and scanned on the photosensitive member 15 at a constant speed in the main scanning direction, and a latent image 1016 is formed on the photosensitive member 15 by scanning of the laser beam, that is, a scanning operation. Is done.

  A beam detect sensor (hereinafter referred to as “BD sensor”) 1017 detects the laser beam reflected and input by the polygon mirror 1002 during the forced lighting period of the LD 100. Then, a beam detect signal (hereinafter referred to as “BD signal”) serving as a reference signal for image formation writing timing for each main scan is output. The BD signal is input to the controller 1027.

  The controller 1027 generates a write sequence from the BD signal, outputs the sequence signal to the FIFO memory 1028, and outputs the control signals cont1 to cont16 to the laser driver 1029.

  The density sensor 1010 detects the toner density on the surface of the photoconductor 15 after development, and outputs the detection result to the controller 1027 as a signal. The controller 1027 calculates the sensitivity of the photoreceptor from the input toner density, and outputs the reference voltages Vcont1 to Vcont16 to the laser driver 1029 so that the optimum exposure amount is obtained.

  FIG. 3 is a diagram showing a circuit configuration example of the LD 100 and the laser driver 1029 shown in FIG.

  The LD 100 has laser diodes LD1, LD2 to LD16 in a package, and the cathode terminals of the LD1, LD2 to LD16 become common terminals and are grounded. The anode terminals of LD1, LD2-LD16 are connected to driver circuits driver1, driver2-driver16, respectively, and a lighting current is supplied from each circuit. The driver 1, driver 2 to driver 16 are the same circuit, and the operation of the driver 1 will be described as a representative.

  The photodiode PD1 is installed at a position where the emitted light of LD1, LD2 to LD16 or a part thereof is irradiated in order to measure the light quantity of LD1, LD2 to LD16. The anode terminal of PD1 is grounded. A bias connected to the power source Vcc is applied to the cathode terminal via the resistor R1, and the cathode terminal becomes a monitor output.

  The cathode terminal of PD1 is connected to the + input terminal of error amplifier OP1. The reference voltage Vcont1 is applied to the negative input terminal of OP1. Vcont1 is generated and supplied by the controller 1027 shown in FIG. The output terminal of OP1 is input to the analog switch SW1. A control signal cont1 is input to a control terminal that controls the operation of SW1. The cont1 is generated and supplied by the controller 1027 shown in FIG.

  The output of SW1 is connected to one end of a capacitor C1 and further input as a control signal for the constant current source CC1. The other end of C1 is grounded. CC1 supplies a current corresponding to the applied voltage from the output. The outputs are connected to the emitter terminals of PNP transistors Q10 and Q11, respectively. The collector terminal of Q10 becomes the output of driver1 and is connected to the anode terminal of LD1. A resistor RD1 is connected to the collector terminal of Q11, and the other end of RD1 is grounded. The signal data1 is input to the base terminal of Q10 via the inverter Q12 and the base terminal of Q11 via the buffer Q13. The data1 is supplied from the FIFO memory 1028 shown in FIG.

  The drivers 2 to 16 other than the driver 1 have the same configuration as the driver 1 described above.

  Next, the operation will be described with reference to FIG.

  First, both cont1 and data1 are output as Hi from the controller 1027 so that the auto power control (APC) mode of the LD1 is set, and cont2 to cont16 and data2 to data16 are output as Lo.

  First, since data1 is Hi, the output of Q12 becomes Lo and Q10 is turned ON. On the other hand, Q11 is turned OFF. When Q10 is turned on, LD1 is lit by the current supplied from CC1. When the light quantity of LD1 increases, the output current of PD1 increases and the voltage input to OP1 decreases. The output of PD1 is compared with Vcont1 by OP1, and the output voltage of OP1 decreases. When the output voltage of OP1 decreases, the output current of CC1 also decreases. When the output current of CC1 also decreases, the light quantity of LD1 also decreases. As described above, this circuit constitutes a negative feedback circuit, and the LD1 is lit with a constant light quantity so that the output of PD1 and Vcont1 have the same voltage.

  In addition, since it operate | moves similarly to the above also in the APC mode of LD2-LD16 other than LD1, those description is abbreviate | omitted.

  Next, the print mode in the image forming apparatus will be described.

  In the print mode, the controller 1027 outputs cont1 to cont16 at Lo and outputs image data for printing as signals data1 to data16. Since cont1 is Lo, SW1 is turned off. For this reason, the voltage in the APC mode is held by C1. Since the voltage of C1 is applied to the control terminal of CC1, the output of CC1 has the same current value as in the APC mode.

  When data1 is Hi, Q10 is turned on and LD1 is lit. On the other hand, when data1 is Lo, Q10 is turned off, so LD1 is turned off. As a result, the laser can be driven to blink by the image data, and image exposure can be performed. In addition, it is known that the semiconductor laser is lit with a constant light amount at the same current value in the same environment, and thus it can be lit with a constant light amount equivalent to the APC mode.

  When data1 is Hi, Q11 is turned off. When data1 is Lo, Q11 is turned on, so that the current supplied from CC1 is applied to RD1. As a result, the current supplied from CC1 is constant without being affected by the status of data1. In general, it is difficult to drive a constant current circuit at a high speed, particularly an operation at several tens of MHz for image formation. However, according to this configuration, Q10 and Q11 require a high speed operation, and CC1 has a high speed. Since no operation is required, image formation is facilitated.

  In addition, since it operates similarly to the above also in the print modes of LD2 to LD16 other than LD1, their description is omitted.

  Next, with reference to FIGS. 4A and 4B, the relationship between the sensitivity of the photoconductor according to the number of beams and the light amount of each beam will be described.

  FIG. 4A shows the case where the optical efficiency is low, that is, the case where the FFP (far field pattern) of the laser is wide and the transmittance and reflectance of the optical component are low. The photoreceptor sensitivity varies in the range of 0.23 to 0.35 including initial variations and durability deterioration. Also, assuming that the maximum light quantity rating of each beam is 1 mW and the minimum light quantity that can be used without image deterioration is 0.3 mW, the light quantity of each beam is within 0.4 mW to 1 mW within the range of sensitivity of the photosensitive member with 16 beams. Therefore, it can be seen that there is no problem if image formation is performed with 16 beams.

  FIG. 4B shows a case where the optical efficiency is high, that is, a case where the FFP (far field pattern) of the laser is narrow and the transmittance and the reflectance of the optical component vary. At this time, when the sensitivity of the photosensitive member is high at 16 beams, the light quantity of each beam is 0.3 mW or less. However, since the characteristics in the case of 10 beams are in the range of 0.3 mW to 0.7 mW, it can be seen that there is no problem when the light quantity is low.

  Next, a sequence for determining the number of beams will be described with reference to FIG.

  In the case of FIG. 4A, first, the controller 1027 forms an image patch for density detection with 16 beams on the photosensitive member, and detects the toner density by the density sensor 1010 (step S501). Next, the controller 1027 determines whether or not the detected toner density is within an appropriate density range (step S502). If it is determined that it is not within the proper range, the controller 1027 calculates a target light amount of the beam that is within the proper density range from the detected toner density (step S503).

  Next, the controller 1027 determines whether or not the target light amount calculated in step S503 is within an appropriate light amount range of 0.3 mW to 1 mW (step S504). In the case of FIG. 4A, a light amount value that is within an appropriate light amount range with 16 beams is calculated. The controller 1027 again forms an image patch for density detection on the photoconductor with the calculated target light amount, and detects the toner density (step S501). The controller 1027 determines whether or not the detected toner density is within an appropriate density range (step S502), and if it is appropriate, the density detection sequence ends. Subsequent image forming processing is performed with the number of beams and the amount of light selected at this time.

  Next, the case of FIG. 4B will be described.

  First, the controller 1027 forms an image patch for density detection with 16 beams on the photoconductor, and detects the toner density by the density sensor 1010 (step S501). Next, the controller 1027 determines whether or not the detected toner density is within an appropriate density range (step S502). If it is determined that it is not within the proper range, the controller 1027 calculates a target light amount of the beam that is within the proper density range from the detected toner density (step S503).

  Next, the controller 1027 determines whether or not the target light amount calculated in step S503 is within an appropriate light amount range of 0.3 mW to 1 mW (step S504). In the case of FIG. 4B, a light amount value that does not fall within the appropriate light amount range with 16 beams may be calculated. In that case, the number of beams is switched to 10 and the light quantity value is calculated again (step S505). Further, it is necessary to keep productivity constant even when the number of beams is switched. As shown in the above equation (1), it can be seen that when the number of beams N is switched, the productivity PS can be kept constant by switching the rotational speed RMS of the polygon motor 1003. FIG. 6 shows the relationship between the number of laser beams and the rotational speed of the polygon motor. As shown in FIG. 6, the rotational speed of the polygon motor 1003 at 16 beams is about 23000 RPM, but is about 36000 RPM at 10 beams. As a result, the controller 1027 switches the rotation speed of the polygon motor from 23000 RPM to 36000 RPM.

  Next, the controller 1027 again forms a density detection image patch on the photosensitive member with the calculated target light amount, the number of beams, and the rotational speed of the polygon motor, and detects the toner density.

  Next, the controller 1027 determines whether or not the detected toner density is in an appropriate density range (step S502), and if it is appropriate, the density detection sequence ends. Subsequent image formation processing is performed at the light amount, the number of beams, and the rotation speed of the polygon motor determined in the above processing.

  Next, the flow of image data during image formation will be described with reference to FIGS. 7 (a) and 7 (b).

  FIG. 7A shows a sequence of image data at the time of image formation with 16 beams shown in FIG. 4A or 4B.

  In FIG. 7A, the numbers in the image data represent the number of lines of image data in the sub-scanning direction. The data are sequentially input to and stored in the FIFO memory 1028 in FIG. 2 from the first line. When a BD signal, which is a writing signal, is input, the image data from the first line to the 16th line are output as data1 to data16, respectively, and 16 lines are exposed simultaneously.

  Next, when the data from the 17th line to the 32nd line are sequentially input, the next BD signal is input, and at the next scanning, the image data from the 17th line to the 32nd line are output as data1 to data16, respectively. Similarly, 16 rows are exposed simultaneously.

  FIG. 7B shows a sequence of image data during image formation with 10 beams shown in FIG.

  In FIG. 7B, the numbers in the image data represent the number of rows of image data in the sub-scanning direction, as in FIG. 7A. The data are sequentially input to and stored in the FIFO memory 1028 in FIG. 2 from the first line. Since the rotation speed of the polygon motor 1003 is faster than that at 16 beams, the BD signal is output when the image data on the 10th row is input. When a BD signal as a writing signal is input, image data from the first line to the tenth line are output from data1 to data10, respectively. Since no data is output from data 11 to data 16, 10 lines are exposed simultaneously. Next, when the data from the 11th line to the 20th line are sequentially input, the next BD signal is input, and the image data from the 11th line to the 20th line is output from data1 to data10 at the next scanning, respectively. Similarly, 10 rows are exposed simultaneously.

  As described above, according to the present embodiment, since the light amount of each beam can be used in the range of 0.3 mW to 0.7 mW, the light amount range of the laser to be used can be narrowed. It is possible to prevent adverse effects such as a decrease in response at the time of light quantity and an increase in spot diameter. Further, it is possible to prevent the productivity from being lowered by switching the driving speed of the polygon motor in accordance with the number of laser beams.

  In the above embodiment, 36000 RPM is close to the limit of the rotational speed of the polygon motor. For this reason, in order to keep productivity constant, exposure with 10 to 16 beams is necessary. Conversely, image formation with a beam number between 10 and 16 beams can also achieve the effects of the present invention.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIG. The image forming apparatus according to the second embodiment of the present invention has the same configuration as that of the image forming apparatus according to the first embodiment, and the same parts as those in the first embodiment are the same. The description thereof will be omitted using the reference numeral. Only differences from the first embodiment will be described below.

  FIG. 8 is a diagram showing the relationship between the laser FFP (far field pattern) corresponding to the number of beams for obtaining the necessary light amount on the surface of the photosensitive member and the light amount of the chip surface of each laser.

  In the figure, when the FFP is large, that is, when the spread angle of light is large, the coupling efficiency of the optical system is lowered, so that the required amount of light on the chip surface of each laser increases. Further, when the light spread angle is small, the coupling efficiency of the optical system is improved, so that the required amount of light on the chip surface of each laser is small. In this case, for 16 beams, when the FFP is approximately 6.6 °, the amount of light on the chip surface of each laser is 0.3 mW. Therefore, the FFP of the laser is measured in advance during assembly adjustment of the scanning exposure apparatus, and stored in a storage device mounted on the scanning exposure apparatus. When the scanning exposure apparatus is mounted on the image forming apparatus main body and image formation is started, the controller 1027 reads the FFP stored in the storage device and predicts how much the chip surface light amount will be.

  For example, if the FFP is larger than about 6.6 ° during image formation, the number of beams is set to 16 and the polygon motor rotation speed is set accordingly, and the amount of light of each beam is set to 0.3 mW or more to form an image. It becomes possible. Further, when the FFP is smaller than about 6.6 °, the number of beams is set to 10, and the polygon motor rotation speed corresponding to the number of beams is set, and the light quantity of each beam can be set to 0.3 mW or more to form an image. Become.

  In the first and second embodiments, the example in which the density sensor 1010 detects the density of the toner image on the photosensitive member in order to determine the light amount of the beam has been described. However, the parameter for determining the light amount is detected. The present invention can be applied to any signal means. For example, it is possible to obtain the same effect even if the amount of light beam to be exposed, the number of beams, and the rotational speed of the polygon motor are determined from a signal obtained by detecting the latent image potential after exposure on the photosensitive member by the potential sensor. .

  When the present invention is not used, it is necessary to use it with a low amount of light. In this case, since it is necessary to supply power in an extremely short time at the time of start-up, the drive circuit becomes complicated and costs increase. Further, even if the problem at the time of driving can be solved, there is a problem that the laser characteristics in the low light quantity region near the threshold value are unstable, and there is a problem that only the countermeasures at the driving are insufficient. It may be difficult to extract a large amount of light as a feature of a VCSEL that can be easily multi-beamed. A normal edge emitter diode can easily obtain a light quantity of several tens of mW or more, whereas a VCSEL can obtain only a light quantity of about 1 to 3 mW.

  Further, as shown in the conventional example, the laser needs a wide light quantity range. In some cases, a range of about 10 times is required. In this case, a 10 mW edge emitter diode can be handled by designing it to be used in the range of 1 mW to 10 mW. In the case of a 1 mW VCSEL, it can be handled by designing it to be used in the range of 0.1 mW to 1 mW. However, when the light quantity is as low as 0.1 mW, it becomes closer to the light quantity of the threshold value, which may be different from the laser characteristic of the high light quantity. For example, the light rise time is fast when the light quantity is high and slow when the light quantity is low. Since the difference in the rising characteristics of the light affects the profile of the exposure potential and the image quality changes, it is difficult to make the image quality uniform. In addition, it affects the spectrum of the light wavelength. When the light intensity is low, the margin (SMSR) with respect to the second peak of the oscillation wavelength is lowered, and the spot on the photoconductor is enlarged. Occurs.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

14, 15, 16, 17 Photoconductor 100 LD
1002 Polygon mirror 1003 Polygon motor 1010 Density sensor 1017 BD sensor 1027 Controller 1028 FIFO memory 1029 Laser driver

Claims (6)

A light source that emits a plurality of beams, a driving unit that rotationally drives the rotating polygon mirror, and a plurality of beams emitted from the light source are deflected by the rotating polygon mirror that is driven to rotate by the driving unit to thereby surface the surface of the photoreceptor. In an image forming apparatus comprising: a scanning exposure unit that performs scanning exposure; and a control unit that controls a rotation speed of the driving unit.
Detection means for detecting the state of an image formed on the surface of the photoreceptor;
Calculating means for calculating a target light quantity of the beam from a detection result by the detection means,
The control unit switches the number of the plurality of beams emitted from the light source and switches the rotation speed of the driving unit when the calculated target light amount is out of a predetermined range. apparatus. A developing means for supplying toner to the electrostatic latent image formed on the surface of the photoreceptor by the scanning exposure means and developing the toner image;
The image forming apparatus according to claim 1, wherein the detecting unit detects a density of a toner image formed on the surface of the photosensitive member by the developing unit.   The image forming apparatus according to claim 1, wherein the detection unit detects a potential of an electrostatic latent image formed on the surface of the photoconductor by the scanning exposure unit. Storage means for storing FFP (far field pattern) of the light source;
The image forming apparatus according to claim 1, wherein the calculation unit calculates a target light amount of the beam based on an FFP stored in the storage unit.   When the target light amount newly calculated by the calculation unit from the detection result by the detection unit is within the predetermined range, the control unit is configured to output the target light amount, the number of beams after switching, and the rotation speed after switching. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled so as to perform image formation using an image forming apparatus. A light source that emits a plurality of beams, a driving unit that rotationally drives the rotating polygon mirror, and a plurality of beams emitted from the light source are deflected by the rotating polygon mirror that is driven to rotate by the driving unit to thereby surface the surface of the photoreceptor. In a control method for an image forming apparatus, comprising: a scanning exposure unit that performs scanning exposure; and a control unit that controls a rotation speed of the driving unit.
A detection step of detecting a state of an image formed on the surface of the photoreceptor by a detection unit;
A calculation step in which the control means calculates a target light amount of the beam from a detection result by the detection means;
And a switching step of switching the number of beams emitted from the light source and switching the rotation speed of the driving unit when the calculated target light amount is out of a predetermined range. Characteristic control method.

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