JP4396667B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus including a plurality of laser emitters.

For example, in the image forming apparatus described in Patent Document 1, two BD (Beam Detect) sensors each for detecting a laser emitter and a laser beam scanning start position (scanning origin) are provided, and the first BD sensor uses the first BD sensor. The scanning start position by one laser emitter is detected, the scanning start position by the second laser emitter is detected by the second BD sensor, and image formation is performed when the scanning start position is detected by the first BD sensor and the second BD sensor. Has started.
JP 2005-10495 A

  However, in the invention described in Patent Document 1, the first laser emitter and the second laser emitter continue to emit laser light until the scanning start position is detected by the first BD sensor and the second BD sensor. Even after the first BD sensor detects the scanning start position by the first laser emitter, the first laser emitter does not stop emitting light until the second BD sensor detects the scanning start position by the second laser emitter. Continue to emit light.

  For this reason, in the invention described in Patent Document 1, since the photosensitive member is unnecessarily exposed even when no image is formed, the photosensitive member is exposed unnecessarily, and the life of the photosensitive member is exhausted early. There is a high risk.

  In view of the above points, an object of the present invention is to prevent the life of a photoconductor from being exhausted at an early stage.

  In order to achieve the above object, according to the present invention, the photosensitive member (510) is exposed by laser light to form an electrostatic latent image, and the electrostatic latent image is electrostatically attracted to the electrostatic latent image. An electrophotographic image forming apparatus for forming an image on a recording medium by transferring the developed developer onto the recording medium, and a plurality of laser light emitters (LD) for emitting laser light and a plurality of laser light emission Deflection scanning means (402) for deflecting and scanning the laser light emitted from the detector (LD), and a plurality of scanning detection means (421, 422) for detecting the laser light along with the deflection scanning by the deflection scanning means (402). Until all of the plurality of scanning detection means (421, 422) detect the laser light at the deflection scanning start position, the light emission amount of the laser light emitter (LD) in the image forming area is set to be a predetermined value or less. Multiple laser emitters Characterized in that it comprises a laser emitting limiting means (700) for controlling the LD).

  As a result, in the present invention, even when the scan start position is detected by only one of the scanning detection means (421, 422) among the plurality of scanning detection means (421, 422), the plurality of scanning detection means (421, 422). Until all of the scanning detection means (421, 422) detect the laser beam at the deflection scanning start position, the light emission amount of the laser emitter (LD) in the image forming area becomes a predetermined value or less, so the photosensitive member (510). Can be prevented from being unnecessarily exposed, and the life of the photoconductor (510) can be prevented from being exhausted early.

  In the invention described in claim 2, when the scanning detection means (421, 422) detects the laser beam, the laser emission limiting means (700) corresponds to the detected laser beam (LD). The energizing current is set to a current smaller than a threshold value at which the laser emitter (LD) starts to emit light.

The number of scanning detection means (421, 422) is desirably the same as the number of types in the deflection scanning direction by the deflection scanning means (402), as in the third aspect of the invention.
In the invention according to claim 3, as in the invention according to claim 4, a laser emitter (LD) that emits a laser beam deflected and scanned in the same direction among a plurality of laser emitters (LD). If the scanning detection means (421, 422) for detecting the deflection scanning start position of the laser beam deflected and scanned in that direction is controlled based on the timing at which the laser beam is detected, the exposure timing can be controlled with high accuracy. be able to.

  In the invention described in claim 5, four photoconductors (510) and four laser emitters (LD) corresponding to black, cyan, magenta and yellow are provided, and the deflection scanning means (402) is 1 Each of the rotary polygon mirrors includes two scanning detection means (421, 422).

  Incidentally, the reference numerals in parentheses for each of the above means are examples showing the correspondence with the specific means described in the embodiments described later, and the present invention is indicated by the reference numerals in the parentheses of the above respective means. It is not limited to specific means.

  In the present embodiment, the image forming apparatus according to the present invention is applied to a tandem electrophotographic image forming apparatus (color laser printer), and this laser printer is used by being connected to a computer. Hereinafter, the present embodiment will be described with reference to the drawings.

1. FIG. 1 is a side sectional view showing the main part of a laser printer 100. The laser printer 100 is installed with the upper side of the paper as the upper side in the direction of gravity, and normally the left side of the paper is used as the front side.

  The housing 103 of the laser printer 100 is formed in a substantially box shape (cubic shape), and on the upper surface side of the housing 103 is a recording medium such as paper or an OHP sheet that is discharged from the housing 103 after printing is completed. A paper discharge tray 105 on which (hereinafter simply referred to as “paper”) is placed is provided.

2. Internal Configuration of Laser Printer The image forming unit 200 is an image forming unit that forms an image on a sheet, and the feeder unit 300 constitutes a part of a conveying unit that supplies the sheet to the image forming unit 200 together with a conveying mechanism 350. The transport mechanism 350 is a transport unit that transports the paper to the four process cartridges 500k, 500y, 500m, and 500c constituting the image forming unit 200.

  Note that the paper on which image formation has been completed by the image forming unit 200 is turned approximately 180 ° upward by an intermediate conveyance roller 380 and a discharge chute (not shown), and then is discharged by the discharge roller 390. The paper is discharged from the discharge unit 107 to the paper discharge tray 105.

2.1. Feeder Unit The feeder unit 300 is provided at the upper side of the paper feed direction in the sheet conveyance direction among the paper feed tray 301 housed in the lowermost part of the housing 103 and corresponding to the end of the paper feed tray 301. A sheet feeding roller 303 that feeds (conveys) the sheet placed on the image forming unit 200, and a sheet fed by the sheet feeding roller 303 is separated by giving a predetermined conveyance resistance to the sheet. The separation pad 305 and the like are configured.

  Then, the paper placed on the paper feed tray 301 is conveyed to the image forming unit 200 disposed substantially in the center of the housing 103 so as to make a U-turn on the front side of the housing 103. Is done.

  Further, in a part of the paper conveyance path from the paper feed tray 301 to the image forming unit 200, the paper is conveyed to the paper conveyed to the image forming unit 200 while being curved in a substantially U shape at a portion that turns in a substantially U shape. A conveying roller 307 that applies force is disposed, and a pressure roller 309 that presses the sheet toward the conveying roller 307 is disposed at a portion facing the conveying roller 307 across the sheet. The pressure roller 309 is pressed toward the conveying roller 307 by an elastic means such as a coil spring (not shown).

  Then, downstream of the conveyance roller 307 in the sheet conveyance direction, the skew of the sheet is corrected by contacting the leading edge of the sheet conveyed by the conveyance roller 307, and then the sheet is further transferred to the image forming unit 200. A registration roller 311 to be conveyed toward the registration roller and a registration roller 313 disposed to face the registration roller 311 are provided. The registration roller 313 is pressed toward the registration roller 311 by an elastic means such as a coil spring (not shown).

2.2. Conveying Mechanism The conveying mechanism 350 includes a driving roller 351 that rotates in conjunction with the operation of the image forming unit 200, a driven roller 353 that is rotatably disposed at a position separated from the driving roller 351, and the driving roller 351 and the driven roller 353. It is composed of a conveyor belt 355 and the like wound between them.

  Then, the conveyance belt 355 rotates with the sheet placed thereon, so that the sheet conveyed from the sheet feeding tray 301 is conveyed in the front-rear direction of the laser printer 100, thereby four process cartridges 500k, 500y, 500m. , 500c sequentially.

In this embodiment, a belt cleaner 360 that removes waste toner adhering to the surface of the conveyance belt 355 is provided below the conveyance mechanism 350.
2.3. Image Forming Unit The image forming unit 200 includes a scanner unit 400, a process cartridge 500, a fixing unit 600, and the like.

  The image forming unit 200 according to the present embodiment is a so-called direct tandem type capable of color printing. In this embodiment, four process cartridges 500k corresponding to four color toners (developer) of black (K), yellow (Y), magenta (M), and cyan (C) from the upstream side in the sheet conveyance direction. , 500y, 500m, and 500c are arranged in series along the paper transport direction.

  The four process cartridges 500k, 500y, 500m, and 500c are the same except for the toner color. Therefore, hereinafter, the four process cartridges 500k, 500y, 500m, and 500c are collectively referred to as a process cartridge 500.

2.3.1. Process Cartridges Since the four process cartridges 500k, 500y, 500m, and 500c differ only in the color of the toner and the others are the same, the structure thereof will be described below taking the process cartridge 500c as an example.

  As shown in FIG. 1, the process cartridge 500 is detachably disposed in the housing 103 below the scanner unit 400. The process cartridge 500 includes a photosensitive drum 510, a charger 520, and a toner container. It has a casing 560 for housing the part 530 and the like.

  The transfer roller 570 is rotatably supported by a main body frame (not shown) on the side opposite to the photosensitive drum 510 with the conveyance belt 355 interposed therebetween. Further, in this embodiment, since the four process cartridges 500k, 500y, 500m, and 500c are housed in the casing 560, these four process cartridges 500k, 500y, 500m, and 500c are integrated into the main body frame. It is attached to and detached from.

  The photosensitive drum 510 forms a photosensitive member that carries an image transferred onto a sheet, and has a cylindrical shape formed by a positively chargeable photosensitive layer whose outermost layer is made of polycarbonate or the like.

  The charger 520 serves as a charging unit that charges the surface of the photosensitive drum 510. The charger 520 is arranged on the rear side of the photosensitive drum 510 so as to face the photosensitive drum 510 at a predetermined interval so as not to contact the photosensitive drum 510. It is installed.

  The charger 520 according to the present embodiment employs a scorotron charger that charges the surface of the photosensitive drum 510 substantially uniformly with a positive charge by performing corona discharge from a charging wire made of tungsten or the like.

  The transfer roller 570 is disposed opposite to the photosensitive drum 510 and rotates in conjunction with the rotation of the conveyance belt 355, and is opposite to the electric charge charged in the photosensitive drum 510 when the sheet passes near the photosensitive drum 510. By applying an electric charge (in this embodiment, a negative charge) to the paper from the side opposite to the printing surface, the transfer means for transferring the toner adhering to the surface of the photosensitive drum 510 to the printing surface of the paper.

  The toner storage unit 530 includes a toner storage chamber 531 that stores toner, a toner supply roller 532 that supplies toner to the photosensitive drum 510, a developing roller 533, and the like. The toner storage unit according to the present embodiment. 530 can be attached to and detached from the main body of the process cartridge 500.

  The toner stored in the toner storage chamber 531 is supplied to the developing roller 533 side by the rotation of the toner supply roller 532, and the toner supplied to the developing roller 533 side is carried on the surface of the developing roller 533. In addition, the thickness of the toner carried by the layer thickness regulating blade 534 is adjusted to be constant (uniform) at a predetermined thickness, and then supplied to the surface of the photosensitive drum 510 exposed by the scanner unit 400. .

2.3.2. Fixing unit The fixing unit 600 is arranged on the downstream side of the photosensitive drum 510 in the paper transport direction, and heats and melts the toner transferred onto the paper. The fixing unit 600 is attached to the main body frame. Removably assembled.

  Specifically, the fixing unit 600 is disposed on the printing surface side of the sheet, and is disposed on the opposite side of the heating roller 610 with the sheet sandwiched between the heating roller 610 that applies toner to the sheet while heating the toner. And a pressure roller 620 that presses the sheet to the heating roller 610 side.

  The heating roller 610 is rotationally driven in synchronization with the developing roller 533, the conveying belt 355, and the like. On the other hand, the pressure roller 620 receives a rotational force from the heating roller 610 via a sheet that contacts the heating roller 610. Followed rotation.

2.3.3. Scanner Unit FIG. 2A is a top view showing a schematic configuration of the scanner unit 400, FIG. 2B is an explanatory view showing laser light deflected by the polygon mirror 402, and FIG. FIG.

  In FIG. 2A, since the reflection mirror is omitted, the optical paths of the laser light Lk and the laser light Ly are shown as developed optical paths in which the return optical path by the reflection mirror is omitted. This is equivalent to the optical path shown in FIG.

The scanner unit 400 is an exposure unit that exposes the surface of the photosensitive drum 510 by irradiating the photosensitive drum 510 with laser light to form an electrostatic latent image.
As shown in FIG. 2, a plurality of (four in this embodiment) laser diodes LDk, LDc, LDm, and LDy (hereinafter referred to as these lasers) that emit laser light are disposed in the casing 401 of the scanner unit 400. A diode is collectively referred to as a laser diode LD.), And a polygon mirror 402 serving as a deflection scanning unit that deflects and scans the laser light emitted from the laser diode LD is provided in the approximate center of the casing 401. Is provided.

  The polygon mirror 402 is a rotary polygon mirror that is rotationally driven by an electric motor 403 (see FIG. 3), and the laser diode LD is a semiconductor that oscillates and emits laser light when a current exceeding a threshold value is applied. It is a laser.

  Incidentally, the laser diode LDk and the laser diode LDm emit laser light to the polygon mirror 402 obliquely upward with respect to a plane (horizontal plane) perpendicular to the reflection surface of the polygon mirror 402, and the laser diode LDc and laser diode LDy. Are arranged at positions where laser light is emitted to the polygon mirror 402 from obliquely below the horizontal plane.

  The laser diode LDk emits laser light for forming a black electrostatic latent image, and the laser light Lk emitted from the laser diode LDk reaches the polygon mirror 402 via the cylindrical lens 404. .

  As shown in FIG. 3, the laser light Lk deflected by the polygon mirror 402 is guided to the front side of the laser printer 100, passes through the fθ lens 405, and is folded back by the reflection mirror 406.

  Thereafter, the laser beam Lk is folded downward by the reflection mirror 407, passes through the toric lens 408k, and is irradiated onto the surface of the black photosensitive drum 510k. At this time, since the polygon mirror 402 is rotating, the laser beam Lk is scanned at high speed on the surface of the photosensitive drum 510k from one end side in the longitudinal direction to the other end side (from the lower side to the upper side in FIG. 2A). Is done.

  The laser diode LDc emits laser light for forming a cyan electrostatic latent image, and the laser light Lc emitted from the laser diode LDc reaches the polygon mirror 402 via the cylindrical lens 404. To do.

  The laser beam Lc is deflected and scanned by the polygon mirror 402, passes through the fθ lens 405, is folded back by the reflecting mirrors 409 and 410, is further folded downward by the reflecting mirror 411, and then the toric lens 408c. Then, the light is irradiated onto the surface of the cyan photosensitive drum 510c while being scanned at high speed.

  The laser diode LDm emits laser light for forming a magenta electrostatic latent image, and the laser light Lm emitted from the laser diode LDm is transmitted to the polygon mirror 402 via the cylindrical lens 412. To reach.

  The laser beam Lm deflected by the polygon mirror 402 is guided to the rear side of the laser printer 100 opposite to the laser beams Lk and Lc, passes through the fθ lens 413, and then forwards by the reflection mirrors 414 and 415. Wrapped.

  Thereafter, the laser beam Lm is folded downward by the reflection mirror 416, passes through the toric lens 408m, and is irradiated onto the surface of the magenta photosensitive drum 510m. At this time, since the polygon mirror 402 is rotating, the laser beam Lm is scanned at high speed on the surface of the photosensitive drum 510m from one end side in the longitudinal direction to the other end side (from the upper side to the lower side in FIG. 2A). The

  The laser diode LDy emits a laser beam for forming a yellow electrostatic latent image, and the laser beam Ly emitted from the laser diode LDy reaches the polygon mirror 402 via the cylindrical lens 412. To do.

  The laser light Ly is deflected and scanned by the polygon mirror 402, passes through the fθ lens 413, is folded back by the reflecting mirror 417, and further folded by the reflecting mirror 418 to the lower side, and then the toric lens 408y. And is irradiated onto the surface of the yellow photosensitive drum 510y while being scanned at high speed.

  Further, at the left end of the front inner wall surface in the casing 401, as shown in FIG. 2A, a first BD (Beam Detect) for detecting laser light at a deflection scanning start position (scanning origin) by the polygon mirror 402 is provided. ) A sensor 421 is disposed, and a second BD sensor 422 is disposed at the left end of the rear side inner wall surface in the casing 401.

  The first BD sensor 421 emits laser light Lk or laser light Lc (this embodiment) that is scanned from the lower side to the upper side in FIG. In the embodiment, it is a light receiving element that receives the laser light Lk), and the second BD sensor 422 is the laser light emitted from the four laser diodes LD and deflected and scanned from the upper side of FIG. This is a light receiving element that receives laser light Lm or laser light Ly (in this embodiment, laser light LDy) scanned downward.

  The laser light Lk and the laser light Lc are applied to the image forming regions of the photosensitive drum 510k and the photosensitive drum 510c based on the timing at which the first BD sensor 421 receives (detects) the laser light Lk. The exposure timing for forming an electrostatic latent image on the photosensitive drum 510 is controlled.

  Similarly, the laser light irradiation period of the laser light Lm and the laser light Ly is based on the timing at which the second BD sensor 422 receives (detects) the laser light LDy. Be controlled.

  That is, the ASIC 700 described later assumes that the laser light has reached the scanning direction end of the image forming area when a predetermined time has elapsed since the first BD sensor 421 and the second BD sensor 422 detected the laser light. The lighting timing of the laser diode LD is controlled based on the data of the image to be formed.

3. Configuration of Control System of Laser Printer FIG. 4 is a block diagram showing the configuration of the control system of the polygon motor 403 and each laser diode LD.

  FIG. 4 shows only the connection relationship between the laser diode LDk and the ASIC (Application Specific Integrated Circuit) 700, but the laser diode LDc is exactly the same as the laser diode LDk. Further, in the case of the laser diode LDm and the laser diode LDy, only the signal of the first BD sensor 421 (first BD signal) is replaced with the signal of the second BD sensor 422, and the others are the same as in FIG.

  The laser diode LDk is housed in the laser diode unit LDp together with the light quantity detection photodiode PD generated by the laser diode LDk. The anode of the photodiode PD is connected to the A / D input port of the ASIC 700 and is variable. It is grounded through a resistor VR1. On the other hand, an LD power control unit 702 is connected to the cathode of the laser diode LDk via a high-speed modulation circuit 701.

  The high-speed modulation circuit 701 switches between short-circuiting or insulation between the laser diode LDk and an LD power control unit 702 (to be described later) based on the black print DATA signal input from the ASIC 700.

  The cathode of the photodiode PD is connected to a 5V power source together with the anode of the laser diode LDk. For this reason, the anode voltage of the photodiode PD (hereinafter referred to as the monitor voltage) changes in accordance with the amount of light of the laser diode LDk.

  The LD power control unit 702 is set by a PWM / A conversion unit 703 that converts the PWM signal input from the ASIC 700 into an analog voltage, and a voltage output from the PWM / A conversion unit 703 and a reference voltage setting unit 704. A comparison circuit error amplifier 705 that amplifies the difference from the reference voltage with a predetermined gain, an LD drive current control circuit 706 that controls the drive current to the laser diode LDk according to the output of the comparison circuit error amplifier 705, and the like. Has been.

  A bias control unit 707 is connected to the cathode of the laser diode LDk in parallel with the high-speed modulation circuit 701 and the LD power control unit 702. The bias control unit 707 converts the PWM signal input from the ASIC 700 into an analog signal. A PWM / A converter 708 that converts the voltage into a voltage, and an LD bias current control circuit 709 that controls the current supplied to the laser diode LDk according to the voltage output from the PWM / A converter 708 are configured. .

  The ASIC 700 inputs a PWM signal corresponding to the monitor voltage input as an analog signal (ANALOG signal) to the LD power control unit 702 when the print DATA signal is ON, that is, when the high-speed modulation circuit 701 is in a short circuit state. Thereby, the drive current of the laser diode LDk is controlled so that the amount of light when the laser diode LDk is turned on becomes a value corresponding to the reference voltage.

  Further, the ASIC 700 gradually increases the current supplied to the laser diode LDk via the bias control unit 707 when the laser diode LDk is turned off, that is, when the high-speed modulation circuit 701 is in an insulating state. A current (hereinafter referred to as a bias current) that does not cause LDk to generate laser light Lk (oscillation light) is detected.

  Normally, this bias current is set to a current smaller than the threshold value of the laser diode LDk. That is, since the bias current is smaller than a threshold value that is a current at which the laser diode LDk starts to emit light, the laser diode LDk does not emit light even when the bias current is applied to the laser diode LDk.

  When the laser diode LDk is turned off, the ASIC 700 supplies the detected bias current via the bias control unit 707 in order to improve the response of the laser diode LDk to the print DATA signal.

  The ASIC 700 receives a first BD signal that is a detection signal of the first BD sensor 421. The ASIC 700 controls an electric motor (polygon motor) 403 that rotates the polygon mirror 402 via a motor drive circuit (not shown).

4). Control of Laser Diode LD As described above, the laser diode LD is turned on (emitted) and turned off, as described above, based on the timing at which the first BD sensor 421 and the second BD sensor 422 detect the laser light (start of laser irradiation in the image forming region ( After detection and determination of the (origin) position, control is performed based on image data to be formed.

  For this reason, the lighting control of the laser diode LD is controlled until the first BD sensor 421 or the second BD sensor 422 detects the laser light Lk or the laser light LDy (hereinafter, this control is referred to as LD start mode control) and the laser. After detecting and determining the irradiation start (origin) position, there is lighting control based on image data to be formed (hereinafter, this control is referred to as print mode control).

  In this embodiment, the light emission amount of the laser diode LD in the image forming area of the photosensitive drum 510 is less than a predetermined amount until both the first BD sensor 421 and the second BD sensor 422 detect the laser light during the LD start mode control. The laser diode LD is controlled so that when the first BD sensor 421 and the second BD sensor 422 detect the laser beam, the lighting control of the laser diode LD is shifted to the printing mode control.

  FIG. 5 is a flowchart showing an outline of LD start mode control in the laser printer 100 according to the present embodiment, and FIG. 6 is a time church showing an outline of LD start mode control. The control flow shown in FIG. 5 is activated (executed) by the ASIC 700 when a print start command is issued from a computer (not shown) to which the laser printer 100 is connected.

Hereinafter, the LD activation mode control will be described with reference to the flowchart shown in FIG.
When a print start command is issued, the electric motor (polygon motor 403) that rotates the polygon mirror 402 starts to rotate, and the energization amount to the laser diodes LDk and LDy gradually increases and the laser diode LD begins to emit light ( S1).

  When a current equal to or higher than the threshold is supplied to the laser diodes LDk and LDy and the laser diode LD starts to emit light, a current equal to or higher than the threshold is supplied to the laser diode LD at a predetermined cycle (S3). As a result, the laser diode LD blinks at a predetermined cycle as shown in the range of the LD start mode in FIG.

  In this case, the period (hereinafter, this period is referred to as a first activation period) is at least once or more while the scanned laser beam is scanned from one end side to the other end side in the scanning direction. Needs to be a cycle in which the laser diode LD is turned on, and as the number of times of light emission increases, it becomes easier for the first BD sensor 421 and the second BD sensor 422 to detect the laser light emitted from the laser diode LD.

  When the laser diodes LDk and LDy are energized in the first period, the detection signals of the first BD sensor 421 and the second BD sensor 422 are detected and confirmed by the ASIC 700 (S5, S7), and the first BD sensor 421 and the first BD sensor 421 It is determined whether or not the laser beams Lk and Lm are detected by any of the 2BD sensors 422 (S9).

  At this time, when it is determined that the first BD sensor 421 detects the laser beam Lk and the second BD sensor 422 does not detect the laser beam LDy (S9: BD1 detection), as shown in FIG. The energization cycle to the diode LDk is changed to a second cycle longer than the first cycle, while the energization cycle to the laser diode LDm is maintained at the first cycle and returns to S1 (S11).

The second period is the same period as the first period or longer than the first period, and is substantially equal to the time required for the laser beam to scan from one end side to the other end side in the scanning direction.
In this embodiment, the laser diode LD is controlled to be lit in the second period from when the laser light is detected by the first BD sensor 421 or the second BD sensor 422 to when the printing mode control is started.

  Further, when the laser beam LDy is detected by the second BD sensor 422 and it is determined that the laser beam Lk is not detected by the first BD sensor 421 (S9: BD2 detection), the energization cycle of the laser diode LDm is the first cycle. On the other hand, the energization cycle to the laser diode LDk is maintained at the first cycle and returns to S1 (S13).

  If it is determined that both the first BD sensor 421 and the second BD sensor 422 have detected the laser light (S9: BD1, BD2 detection), all the laser diodes LD are controlled to be turned on by the printing mode control. Printing is started (S15, S17).

If no laser light is detected by any of the first BD sensor 421 and the second BD sensor 422 (S9: NO), the process returns to S1.
5). Features of the Laser Printer 100 According to the Present Embodiment In this embodiment, the laser in the image forming area of the photosensitive drum 510 until both the first BD sensor 421 and the second BD sensor 422 detect laser light during the LD start mode control. The laser diode LD is controlled so that the light emission amount of the diode LD becomes a predetermined value or less, and when both the first BD sensor 421 and the second BD sensor 422 detect laser light, the lighting control of the laser diode LD is shifted to the printing mode control. Therefore, it is possible to prevent the photosensitive drum 510 from being irradiated with laser light more than necessary during the LD start mode control.

Therefore, it is possible to prevent the photosensitive drum 510 from being unnecessarily exposed, and thus it is possible to prevent the life of the photosensitive drum 510 from being exhausted early.
6). Correspondences between Invention Specific Items and Embodiments In this embodiment, the laser diode LD corresponds to the laser emitter described in the claims, and the polygon mirror 402 corresponds to the deflection scanning means described in the claims. The first BD sensor 421 and the second BD sensor 422 correspond to the scanning detection means described in the claims, and the ASIC 700 corresponds to the laser emission limiting means described in the claims.

(Other embodiments)
In the above-described embodiment, the laser diode LD is blinked in the first period before the laser beam is detected by the first BD sensor 421 or the second BD sensor 422. However, the present invention is not limited to this. Alternatively, the laser diode LD may be continuously turned on by continuously supplying a current equal to or higher than the threshold value.

  In the above-described embodiment, after the laser beam is detected by the first BD sensor 421 or the second BD sensor 422, the laser diode LD is blinked in the second period until the print mode control is started. The present invention is not limited to this. For example, after the laser beam is detected by the first BD sensor 421 or the second BD sensor 422, the energization current may be less than the threshold until the print mode control is performed.

  In the above-described embodiment, the first BD sensor 421 is disposed at the left end of the front inner wall surface and the second BD sensor 422 is disposed at the left end of the rear inner wall surface in the casing 401. However, the second BD sensor 422 may be disposed at the right end of the rear side inner wall surface.

  Further, in the above-described embodiment, there are two BD sensors that constitute the scanning detection means, but the present invention is not limited to this, and the same number of BD sensors as the laser diodes LD may be provided.

  In the above-described embodiment, the first BD sensor 421 is disposed on the scanning start side and the second BD sensor 422 is disposed on the scanning end side. However, the present invention is not limited to this, for example, The first BD sensor 421 is disposed on the scanning end side, the second BD sensor 422 is disposed on the scanning start side, or both the first BD sensor 421 and the second BD sensor 422 are disposed on the scanning start side or the scanning end side. May be.

  Further, the present invention is not limited to the above-described embodiment as long as it matches the gist of the invention described in the claims.

1 is a side sectional view showing a main part of a laser printer 100 according to an embodiment of the present invention. (A) is a top view showing a schematic configuration of the scanner unit 400, and (b) is an explanatory diagram showing laser light deflected by the polygon mirror 402. 2 is a cross-sectional view of a scanner unit 400. FIG. It is a block diagram showing the structure of the control system of the polygon motor 403 and each laser diode LD. 4 is a flowchart showing an outline of LD start mode control in the laser printer 100 according to the present embodiment. It is a time church which shows the outline | summary of LD starting mode control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Laser printer, 103 ... Housing | casing, 105 ... Paper discharge tray, 107 ... Discharge part,
200: Image forming unit, 300: Feeder unit, 301: Paper feed tray,
303: Paper feed roller, 307 ... Conveyance roller, 309 ... Pressure roller,
311: Registration roller, 313: Registration roller, 350: Conveying mechanism,
351: Driving roller, 353: Driven roller, 355 ... Conveying belt,
360 ... belt cleaner, 390 ... discharge roller, 400 ... scanner unit,
402 ... polygon mirror, 403 ... polygon motor,
403 ... Electric motor (polygon motor), 404 ... Cylindrical lens,
405: fθ lens, 407: reflection mirror,
408c, 408k, 408m, 408y ... toric lens,
409 ... reflecting mirror, 411 ... reflecting mirror, 412 ... cylindrical lens,
413 ... fθ lens, 414 ... reflection mirror, 416 ... reflection mirror,
417 ... reflecting mirror, 418 ... reflecting mirror, 421 ... first BD sensor,
422 ... 2nd BD sensor, 500 ... Process cartridge, 510 ... Photosensitive drum,
520: Charger, 530: Toner container, 531: Toner container,
532 ... Toner supply roller, 533 ... Development roller, 534 ... Layer thickness regulating blade,
560: casing, 570: transfer roller, 600: fixing unit,
610 ... Heating roller, 620 ... Pressure roller, 701 ... High-speed modulation circuit,
702 ... LD power control unit, 703 ... PWM / A conversion unit, 704 ... reference voltage setting unit,
705 ... Comparison circuit error amplifier, 707 ... Bias controller,
708 ... PWM / A converter, 709 ... LD bias current control circuit,
LD ... laser diode, PD ... photodiode, VR1 ... variable resistor.

Claims (5)

An electrophotographic image in which the photosensitive member is exposed to laser light to form an electrostatic latent image, and the developer electrostatically attracted to the electrostatic latent image is transferred to the recording medium to form an image on the recording medium. A forming device,
A plurality of laser emitters for emitting laser light;
Deflection scanning means for deflecting and scanning laser light emitted from the plurality of laser emitters;
A plurality of scanning detection means for detecting laser light in accordance with the deflection scanning by the deflection scanning means;
Until all of the plurality of scanning detecting means detect laser light at the deflection scanning start position, the plurality of laser light emitting devices so that the light emission amount of the laser light emitting device in the image forming region becomes a predetermined amount or less. An image forming apparatus comprising: a laser emission limiting unit that controls   When the scanning detection unit detects a laser beam, the laser emission limiting unit is configured to set an energization current to the laser emitter corresponding to the detected laser beam to a current smaller than a threshold at which the laser emitter starts to emit light. The image forming apparatus according to claim 1.   3. The image forming apparatus according to claim 1, wherein the same number of scanning detection units as the number of types in the deflection scanning direction by the deflection scanning unit are provided.   Among the plurality of laser emitters, the operation of the laser emitter that emits laser light deflected and scanned in the same direction is performed by deflecting and scanning the laser light deflected and scanned in the direction of the plurality of scanning detection means. The image forming apparatus according to claim 3, wherein the scanning detection unit that detects the start position is controlled based on the timing at which the laser beam is detected. Four photoreceptors and four laser emitters corresponding to black, cyan, magenta and yellow are provided,
The deflection scanning means is composed of one rotating polygon mirror,
The image forming apparatus according to claim 1, wherein two scanning detection units are provided.

Images