JP2008026539A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow an image forming device to be matched to a light receiving quantity allowance range of a light detection means without modifying an individual base light quantity of an optical beam when forming images on an image carrier by a plurality of the optical beams. <P>SOLUTION: The total light emitting quantity of a surface light emitting laser array 50 when passing an SOS sensor 78 is modified by the number of lighting of a light emitting part 50A, i.e. adjusted by setting of turning-on or off without adjusting a light quantity of each light emitting part 50A and is within a range of the light receiving quantity allowance range possessed by the SOS sensor 78. Thereby a gain switching amplifier or the like is unnecessary, and the comparatively inexpensive SOS sensor in which the light receiving quantity allowance range is narrow can be applied without considering the light emitting quantity based on a reference voltage when practically performing image forming processing. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that includes a plurality of light sources and forms an image by scanning a plurality of light beams emitted from the plurality of light sources on an image carrier.

  Conventionally, a light beam emitted from a light source is deflected by a rotating polygon mirror that rotates at high speed, and the deflected light beam is scanned onto an image carrier such as a photosensitive drum (the deflection is the main scanning, the photosensitive member). An electrostatic latent image is formed by the sub-scanning of the drum, and an image (for example, a toner image) obtained by developing the electrostatic latent image with a developer such as toner is transferred to a recording medium to form an image. Image forming apparatuses such as digital copying machines and printers are known.

  The main scanning is repeatedly executed. At this time, light detection is performed on the optical path of the light beam at both ends of the image forming area, in particular, on the upstream side of the image forming area in order to match the writing (image data output timing). A sensor is provided, and the writing start timing of the image forming area is controlled based on the light receiving timing of the light detection sensor.

  Here, the currently applied light detection sensor has a narrow dynamic range, that is, a usable light amount range. For this reason, it is necessary to set the use range in a range that is not less than the amount of light that can be detected by the light detection sensor as the lower limit value of the light source and less than or equal to the amount of light that is not affected by frame reflection or the like. That is, when the light amount falls below the lower limit, detection timing variation (jitter) occurs, and when the light amount exceeds the upper limit, light reception due to frame reflection exists in addition to the original light reception, and a detection error occurs.

  For this reason, depending on the set light quantity, measures such as gain switching are applied to the light detection sensor (see Patent Document 1).

  However, in Patent Document 1, it is necessary to newly add an amplifier to the light detection sensor (SOS sensor) in order to switch the gain according to the amount of light, which increases the number of components, complicates control, and increases costs. Connected.

Further, as related technologies mainly for control on the light source side, when passing through a synchronization signal generating means (light beam position detecting means) based on an operation signal for adjusting the intensity of a laser beam, and when scanning a light source It has been proposed to change the intensity (light quantity) with (see Patent Documents 2 and 3). Note that Patent Document 2 and Patent Document 3 are based on the premise that there is a single light source.
JP 2001-296489 A JP-A-4-204671 JP-A-6-270460

  However, in Patent Document 2 and Patent Document 3, the period from the passage of the synchronization signal generation means (light beam position detection means) to the image formation based on the image data on the image carrier is limited, In particular, the faster the processing speed, the shorter the period, and the light amount adjustment control may not be in time. In particular, in Patent Document 3, when APC (auto power control) for obtaining the first light amount is performed, APC must be performed from the light beam detecting means (SOS) to the start of writing. The control time for switching is insufficient.

  In consideration of the above facts, the present invention provides a light detection unit disposed outside the image forming area without changing the reference light quantity of each light beam when forming an image on the image carrier with a plurality of light beams. An object of the present invention is to obtain an image forming apparatus that can be adjusted to a light reception amount allowable range.

  The present invention comprises an optical scanning device that outputs a plurality of light beams while deflecting them in the main scanning direction, scans the light beam emitted from the optical scanning device onto an image carrier, and forms an electrostatic latent image. An image forming apparatus for forming an image by developing, wherein a light detection unit provided on a scanning optical path of the plurality of light beams and a light beam detection timing by the light detection unit A scanning start timing setting means for setting a scanning start timing for the light detection means, a light beam number determination means for determining the number of light beams to be turned on when passing through the light detection means, and the light beam when passing through the light detection means. Lighting control means for lighting the number of light beams determined by the number determining means.

  According to the present invention, the number of light beams when passing through the light detection means is determined by the light beam number determination means. At the time of image formation processing, the scanning start timing is set based on the light beam detection timing by the light detection means. At this time, the lighting control means turns on the number of light sources determined by the light beam number determination means when passing through the light detection means.

  This limits the number of light beams that are turned on when passing through the light detection means, even if the amount of light by the plurality of light beams during image formation deviates from the light reception amount allowable range of the light detection means. It is possible to keep within the allowable range, and it is possible to prevent erroneous detection due to variations in light amount, reflection, and the like. In other words, it is possible to apply an inexpensive light detection means having a narrow light receiving amount allowable range.

  In the above invention, there is further provided a reference light amount setting unit for setting a reference light amount at the time of image formation, and the light beam number determining unit determines the number of light beams based on the light amount set by the reference light amount setting unit. It is characterized by that.

  The reference light amount varies depending on the model of the image forming apparatus. Further, the reference light amount changes with time even in the same model. Therefore, by determining the number of light beams based on the light amount set by the reference light amount setting means, it is possible to always keep within the light reception amount allowable range of the light detection means.

  Further, the present invention is characterized in that a light beam for exposing a different object to be scanned is incident on the light detection means.

  In order to realize the present invention, a plurality of light beams are indispensable. As a structure of the image forming apparatus, a light beam for exposing a plurality of image carriers (scanned bodies) is guided to the same light detection means. This is possible without using a special back image such as a plurality of light sources.

  As described above, according to the present invention, the light detecting means disposed outside the image forming area can be used without changing the individual light amount or a part of the reference light amount when exposing the light detecting means with a plurality of light beams. It has an excellent effect that it can be adjusted to the light receiving amount allowable range.

  As shown in FIG. 1, an image forming apparatus 10 according to the present embodiment includes a photosensitive drum 12 as an image carrier. The photosensitive drum 12 rotates in a direction indicated by an arrow A at a predetermined speed by a driving force of a driving unit such as a motor (not shown). A charger 14 for charging the peripheral surface of the photosensitive drum 12 is provided above the photosensitive drum 12.

  A light beam scanning device 16 is disposed above the charger 14. Although details will be described later, the light beam scanning device 16 is configured to emit a plurality of light beams from a light source, modulates the plurality of light beams according to an image (on / off control), Deflection is performed in the main scanning direction, and the circumferential surface of the photosensitive drum 12 is scanned (main scanning) in the axial direction of the photosensitive drum 12. As a result, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 12.

  A developing unit 18 is disposed on the side of the photosensitive drum 12. The developing device 18 includes a developing roller 20 and stores toner therein, and the developing roller 20 attaches the toner to the electrostatic latent image formed on the peripheral surface of the photosensitive drum 12 and develops the toner.

  An endless intermediate transfer belt 24 is disposed substantially below the photosensitive drum 12. The intermediate transfer belt 24 is wound around rollers 26, 28, and 30, arranged so that the peripheral surface thereof is in contact with the peripheral surface of the photosensitive drum 12, and rotated in the direction of arrow B.

  At the contact position of the photosensitive drum 12, a transfer device 32 is disposed on the opposite side of the photosensitive drum 12 with the intermediate transfer belt 24 interposed therebetween, and serves as a primary transfer portion.

  When the developed toner image on the peripheral surface of the photosensitive drum 12 reaches the primary transfer portion, it is transferred to the intermediate transfer belt 24 by the transfer device 32.

  On the downstream side of the transfer position on the peripheral surface of the photosensitive drum 12 in the rotational direction, the neutralization / static discharge function has a function of discharging the peripheral surface of the photosensitive drum 12 and a function of removing unnecessary toner remaining on the peripheral surface. A cleaner 22 is disposed. After the transfer, the area carrying the transferred toner image on the peripheral surface of the photosensitive drum 12 is cleaned by the charge eliminating / cleaning device 22.

  A tray 34 is disposed below the intermediate transfer belt 24, and a large number of sheets P as recording media are accommodated in the tray 34 in a stacked state.

  A take-out roller 36 is disposed obliquely above and to the left of the tray 34 in FIG. 1, and a roller pair 38 and a roller 40 are sequentially arranged on the downstream side in the take-out direction of the paper P by the take-out roller 36. The uppermost recording sheet in the stacked state is taken out from the tray 34 by the take-out roller 36 being rotated, and is conveyed by the roller pair 38 and the roller 40 at the same rotational speed as the intermediate transfer belt 24. A registration sensor 45 is disposed on the upstream side of the intermediate transfer belt 24 in the conveyance path of the paper P. The registration sensor 45 detects the leading and trailing edges of the paper P in order to detect the conveyance timing of the paper P and the paper size of the paper P.

  Further, a transfer device 42 is disposed on the opposite side of the roller 30 with the intermediate transfer belt 24 interposed therebetween, and serves as a secondary transfer portion. The paper P conveyed by the roller pair 38 and the roller 40 is sent to a secondary transfer portion between the intermediate transfer belt 24 and the transfer device 42, and the toner image formed on the image forming surface of the intermediate transfer belt 24 is transferred. Transferred by the device 42.

  A fixing device 44 having a heating roller and a pressure roller is disposed downstream of the secondary transfer portion (transfer device 42) in the conveyance direction of the paper P. The paper P on which the toner image is transferred is The transferred toner image is melted and fixed by the fixing device 44 and then discharged to the outside of the image forming apparatus 10 and placed on a discharge tray (not shown).

  Next, the light beam scanning device 16 will be described with reference to FIG. The light beam scanning device 16 includes a surface emitting laser array (hereinafter referred to as “LD” as necessary) 50 that emits a light beam from a plurality of (four shown in FIG. 2) light emitting units 50A.

  The surface emitting laser array 50 has various arrangements depending on the number of the light emitting portions 50A, but is generally a matrix of a plurality of columns and a plurality of rows. For example, as shown in FIG. In the case of the surface emitting laser array 50 having the light emitting portion 50A, if the vertical direction is a column and the horizontal direction is a row, four columns and eight rows may be arranged so that the outline is a substantially parallelogram.

  A collimator lens 52 is disposed on the light beam emission side of the surface emitting laser array 50. The light beam emitted from the surface emitting laser array 50 is made into a substantially parallel light beam by the collimator lens 52 and then enters the cylindrical lens 62. The cylindrical lens 62 is a convex lens having power in the sub-scanning direction.

  Since the surface emitting laser array 50 does not emit a light beam from the side opposite to the side from which the light beam used for exposure is emitted, a light quantity sensor (not shown) is provided in the light beam emitting direction, and the light quantity of the light beam is provided. Is detected to perform light amount control (APC).

  The light beam that has passed through the cylindrical lens 62 is incident on the reflecting mirror on the circumferential surface of the rotary polygon mirror 66 that rotates in the direction of arrow C at a predetermined rotation speed by a driving force of a motor (not shown) and is deflected. The deflected light beam is corrected by the fθ lens 70 so as to scan at a constant speed, and is irradiated onto the peripheral surface of the photosensitive drum 12. At the same time, the photosensitive drum 12 rotates in the sub-scanning direction (arrow D direction) to form an image.

  Further, a pickup mirror 76 is disposed on the light beam emission side of the fθ lens 70 at a position corresponding to a scanning start side end (SOS: Start Of Scan) in the light beam scanning range. An SOS sensor 78 as light detection means is disposed on the light beam emission side.

  When the light beam emitted from the surface emitting laser array 50 reflects the incident beam in the direction corresponding to the SOS, the reflecting surface of the rotary polygon mirror 66 reflects the light beam. Then, the light is reflected by the pickup mirror 76 and enters the SOS sensor 78.

  When the light beam is incident, the SOS sensor 78 outputs a main scanning synchronization signal. This signal is used to modulate the light beam scanned on the circumferential surface of the photosensitive drum 12 as the rotary polygon mirror 66 is rotated to form an electrostatic latent image. Used to synchronize the write timing).

  Here, the SOS sensor 78 outputs a predetermined signal (electrical signal) when a light beam is incident, but the received light amount has a predetermined allowable range (received light amount allowable range) (FIG. 3 ( See B)), if deviating from this, an accurate output signal may not be obtained.

  At this time, an appropriate output can be obtained as long as it is within the allowable light receiving amount range of the SOS sensor 78 itself.

  However, if light with an amount of light exceeding the upper limit of the light reception amount allowable range is input, light from ambient reflection (frame reflection) is input, resulting in detection timing variations and unintended detection signals. There is. In addition, if light that falls below the lower limit of the light reception amount allowable range is input, it is easily affected by jitter, and the exposure timing varies. Furthermore, when the light quantity decreases, it becomes impossible to obtain a detection signal.

  Therefore, in the present embodiment, all the light emitting units 50A emit light during image formation, and when light is input to the SOS sensor 78, the number of light beams that expose the SOS sensor 78 in the surface emitting laser array 50 is changed. Controlled to do.

  Specifically, as shown in FIG. 3A, among the 32 light emitting units 50A, eight light emitting units 50A for one column are designated as the light emitting units 50A that are lit when passing through the SOS sensor 78. Of these, the number is set according to the reference light quantity based on the specifications of the image forming apparatus 10.

  Table 1 is a setting correspondence table for the number.

  As can be seen from Table 1, by determining the set number of light emitting units 50A (the number of light emitting units 50A that are turned on when passing through the SOS sensor 78) in accordance with the respective light amount setting values, the SOS sensor 78 is determined. It can be seen that the amount of incident light is within the range of the received light amount allowable range (60 to 100 μW).

  FIG. 4 is a control block of a light source emission control system including a function for determining the set number of the light emitting units 50A.

  Note that this control block diagram is only divided into blocks according to functions, and does not limit the hardware configuration. A plurality of blocks or all blocks may be configured with a single IC chip, A control program may be set up to execute control.

  The SOS sensor 78 is connected to the writing start timing setting unit 100, and sends an electrical signal corresponding to the detected light to the writing start timing setting unit 100.

  A video memory 102 is connected to the write timing setting unit 100.

  The writing timing setting unit 100 outputs an image writing timing signal for each main scanning line of image data (bitmap data) stored in the video memory 102 to the video memory 102. Note that a video clock unit 104 is connected to the write timing setting unit 100 and the video memory 102, and the write timing setting unit 100 and the video memory 102 are synchronized by the video clock 104.

  The video memory 102 is connected to the LD driving unit 106. The LD driving unit 106 is a driver that controls turning on / off of each light emitting unit 50A of the surface emitting laser array 50, and video data corresponding to each light emitting unit 50A is input from the video memory 102 at a predetermined timing. become.

  A surface emitting laser array 50 is connected to the LD driving unit 106, and lighting (extinguishing) control is executed based on the video data.

  Here, a reference voltage setting unit 108 for setting the amount of exposure light is connected to the LD driving unit 106.

  The LD driving unit 106 causes each light emitting unit 50A to emit light based on the reference voltage set in the reference voltage setting unit 108, and executes image forming processing.

  On the other hand, when passing through the SOS sensor 78, as described above, the number of light emitting units 50A to be lit is determined according to the light amount setting value. In the present embodiment, the light emitting unit 50A is connected to the reference voltage setting unit 108. It is set by the SOS exposure beam setting unit 110. The set number of light emitting units 50 </ b> A is sent to the LD driving unit 106, and the set number of light emitting units 50 </ b> A are turned on at the timing of passing through the SOS sensor 78.

  The operation of the present embodiment will be described below.

  When there is an image formation instruction, rotation of the rotary polygon mirror 66 is started, the photosensitive drum 12 is rotated at a predetermined speed, and the intermediate transfer belt 24 is driven.

  When the photosensitive drum 12 is stabilized at a predetermined speed, the video clock unit 104 is activated and image formation scanning control is started.

  Thereafter, emission of a light beam is started from each light emitting unit 50 </ b> A of the surface emitting laser array 50, and image data is read from the video memory 102 to the LD driving unit 106 line by line.

  Then, with the timing at which the main scanning synchronization signal is input from the SOS sensor 78 as a reference, a modulation signal is generated based on the read image data, and lighting control of each surface emitting unit 50A of the surface emitting laser array 50 is performed.

  This light beam is made into a substantially parallel light beam by the collimator lens 52 and then enters the cylindrical lens 62.

  The light beam transmitted through the cylinder lens 62 is deflected by a rotating polygon mirror 66 rotating at a predetermined speed, and the deflected light beam is corrected by the fθ lens 70 so as to scan at a constant speed. Irradiated on the surface.

  As a result, 32 scanning lines are simultaneously scanned on the circumferential surface of the photosensitive drum 12 for each scan, and an electrostatic latent image is formed on the circumferential surface of the photosensitive drum 12. The electrostatic latent image is developed as a toner image by the developing device 18, and the toner image is transferred by the transfer device 32 in the primary transfer portion and transferred by the transfer device 42 in the secondary transfer portion, and an image is recorded on the paper P. The paper P is melted and fixed on the paper P by the fixing device 44 and discharged.

  By the way, in the present embodiment, when the light beam passes through the SOS sensor 78, not all the light emitting units 50 </ b> A are lit, but a specific number is lit and is within the light receiving amount allowable range of the SOS sensor 78. Is maintained.

  In the following, a flow at the time of a print instruction including control for setting the number of light emitting units 50A when passing through the SOS sensor 78 will be described according to the flowchart of FIG.

  In step 200, it is determined whether or not a print job execution instruction has been issued. If the determination is negative, this routine ends.

  If an affirmative determination is made in step 200, the process proceeds to step 202 to determine whether it is time to execute process control. If an affirmative determination is made, the process proceeds to step 204 to execute a process control (process control) process. The process proceeds to step 206. If the determination at step 200 is negative, the process proceeds to step 206.

  In step 206, it is determined whether or not the reference voltage has been changed by the process control process. If an affirmative determination is made, the process proceeds to step 208 and the reference voltage Vref. Based on the above, the number of light emitting units 50A for the SOS sensor 78 is read (for example, read based on a database such as Table 1), and the process proceeds to step 210.

  In step 210, if it is determined whether or not the number of the read light emitting units 50A is changed in the currently set number and an affirmative determination is made, the process proceeds to step 212 to set the number of light emitting units 50A. Is changed to step 214. If a negative determination is made in step 206 and a negative determination is made in step 210, the process proceeds to step 214.

  In step 214, printing is performed (based on the above-described processing flow), and the process proceeds to step 216.

  In step 216, it is determined whether or not the job is completed. If the determination is negative, the process returns to step 202 and the above steps are repeated. If the determination at step 216 is affirmative, this routine ends.

  As described above, in the present embodiment, the total light emission amount of the surface emitting laser array 50 when passing through the SOS sensor 78 is changed depending on the number of lighting of the light emitting units 50A, that is, not the light amount adjustment of each light emitting unit 50A. The SOS sensor 78 is adjusted so as to be within the allowable range of the received light amount. As a result, a gain switching amplifier or the like is unnecessary, and it is possible to apply a relatively inexpensive SOS sensor with a narrow light reception amount allowable range without considering the light emission amount based on the reference voltage when actually performing image formation processing. It becomes possible.

  At this time, it is preferable to set the number of the light emitting units 50A so that the amount of light incident on the SOS sensor 78 is close to the center value (80 μW) of the range of allowable light reception amount (see Table 1).

  Further, since it is not necessary to worry about the upper limit of the light amount by turning off the light beam with the reference light amount, the SOS sensor 78 having a relatively high gain can be applied. As a result, even if the input light amount is lowered, jitter is reduced. No longer increases rapidly (see FIG. 6). In other words, jitter on the low light amount side can be reduced.

(Modification)
FIG. 7 shows a light beam scanning device 16A of the image forming apparatus according to a modification of the present embodiment.

  A feature of the light beam scanning device 16A according to this modification is that a plurality of light beams are simultaneously incident on a single rotary polygon mirror 150, and the light beams after passing through the fθ lens 152 are different from the photosensitive drums 154 and 156. An optical system for guiding to (see FIG. 7B) is provided.

  FIG. 7A shows a part of the light beam scanning 16A, and the light beam scanning device 16A of FIG. 7A corresponds to image data of black (k) color and cyan (C) color. Is. That is, a light beam scanning device (not shown) having the same structure corresponding to the image data of other colors, magenta (M) and yellow (Y) is present.

  The laser light emitting array 50 attached to the circuit board 160 is irradiated with light beams from a plurality of light emitting units, passes through the collimator lens 162, and is decomposed into reflected light and transmitted light by the half mirror 164.

  The reflected light is input to the monitor photodiode (MPD) 168 via the lens 166, and the amount of light is adjusted in the process control process.

  The transmitted light that passes through the half mirror 164 enters the rotary polygon mirror 150 through the cylindrical lens 170, and the reflected light (scanning light) passes through the fθ lens 152.

  Here, a part of the light beam transmitted through the fθ lens 152 is incident on the cyan (C) cylindrical mirror 176 via the reflection mirrors 172 and 174 and guided to the cyan (C) photosensitive drum 154. Is done.

  The other part of the light beam transmitted through the fθ lens 152 is incident on the black (k) cylindrical mirror 180 via the reflection mirror 178 and guided to the black (k) photosensitive drum 156. .

  At this time, the light beam for black (k) is incident on the SOS sensor 78, and the light beam for cyan (C) depends on the scanning timing of the light beam for black (k) (synchronization). Will do.

  Even if a light source for exposing a single image carrier (scanned body) does not have a plurality of beams, a light beam for exposing a different scanned body is incident on the SOS sensor, thereby forming a plurality of beams on the SOS sensor. It is possible to change the lighting beam according to the reference light quantity. With such a configuration, it is possible to use an inexpensive SOS sensor having a narrow range of received light quantity, which is an effect of the present invention, without using a surface emitting laser.

1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. It is a schematic block diagram of the light beam scanning apparatus which concerns on this Embodiment. It is the figure which showed the relationship between a surface emitting laser array and a SOS sensor. It is a light emission control functional block diagram including the control for selecting the number of the light emission parts of a surface emitting laser array. It is a flowchart which shows the print control routine including the control which selects the number of the light emission parts of a surface emitting laser array. It is a light quantity on a SOS sensor based on the level of a gain, and a jitter characteristic figure. It is a schematic block diagram of the image forming apparatus which concerns on a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Photosensitive drum (Image carrier)
16 Optical beam scanning device (optical scanning device)
50 surface emitting laser array 50A light emitting unit 66 rotating polygon mirror 78 SOS sensor (light detection means)
100 Writing timing setting unit (scanning timing setting means)
102 Video memory 104 Video clock unit 106 LD drive unit (lighting control means)
108 Reference voltage setting unit 110 SOS exposure beam setting unit (light beam number determining means)

Claims (3)

An optical scanning device that outputs a plurality of light beams while deflecting them in the main scanning direction, scans the light beam emitted from the optical scanning device on an image carrier, forms an electrostatic latent image, and develops it. An image forming apparatus for forming an image,
Photodetection means provided on the scanning optical path of the plurality of light beams;
Scanning start timing setting means for setting a scanning start timing for the image formation based on a light beam detection time by the light detection means;
A light beam number determining means for determining the number of light beams to be turned on when passing through the light detecting means;
Lighting control means for lighting the number of light beams determined by the light beam number determining means when passing through the light detection means;
An image forming apparatus. A reference light amount setting means for setting a reference light amount at the time of image formation;
The image forming apparatus according to claim 1, wherein the light beam number determination unit determines the number of light beams based on the light amount set by the reference light amount setting unit.   The image forming apparatus according to claim 1, wherein light for exposing a different object to be scanned is incident on the light detection unit.

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