JP2008009025A - Scanning exposure apparatus and image forming apparatus furnished with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an adverse effect of a large diameter of a rotating polygon mirror and stray light in a configuration in which the detection of the light quantity of a laser element and the detection of a light beam for synchronization control are carried out with one light detection sensor. <P>SOLUTION: A beam reflection region for synchronization control on which a light beam for synchronization control is reflected is provide on the front side in the rotating direction, and a beam reflection region for light quantity detection on which a light beam for light quantity detection is reflected is provide on the rear side in the rotating direction, both on the same reflection face 51 of the rotating polygon mirror 22, interposing a beam reflection region for image formation on which a light beam for forming an image is reflected. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a scanning exposure apparatus in which a light detection sensor disposed in the vicinity of a light source is used for both the purpose of detecting the light quantity of the light source and the use of detecting a light beam for synchronization control, and an image forming apparatus provided with the same It is about.

  In an image forming apparatus (such as a printer, a facsimile machine, a copying machine, and a multi-function machine) that forms an image on recording paper by an electrophotographic process, a light beam generated by a laser element is used to form a latent image on a photoconductor. There is provided a scanning exposure apparatus that deflects with a rotating polygon mirror and scans the photosensitive member. In this scanning exposure apparatus, in order to keep constant the light quantity of the laser element that fluctuates according to environmental changes such as temperature, light quantity control is performed to detect the actual light quantity of the laser element and adjust the drive current of the laser element. In addition, the scanning timing is adjusted by detecting the return beam that is returned by reflecting the light beam emitted from the laser element with a mirror so that a predetermined image forming area on the photosensitive member is appropriately exposed. Synchronous control is performed.

Such a scanning exposure apparatus generally has a configuration in which a light detection sensor that detects the light amount of a laser element for light amount control and a light detection sensor that detects a light beam for synchronous control are provided separately. However, in order to reduce the cost by reducing the number of parts, there is known a technique in which one light detection sensor is used for both the purpose of detecting the light quantity of a laser element and the purpose of detecting a light beam for synchronous control. (See Patent Documents 1, 2, and 3).
Japanese Patent No. 2988682 (FIG. 3) Japanese Patent Publication No. 5-85100 (Fig. 1) Japanese Patent Laid-Open No. 4-146465 (FIGS. 1 and 2)

  However, in the configuration in which one light detection sensor is used for both the detection of the light amount of the laser element and the detection of the light beam for synchronization control as described above, it is difficult to simultaneously perform the respective detection operations. Therefore, it is necessary to perform these detection operations at different timings. On the other hand, the reflecting surface of the rotary polygon mirror is inferior to the central portion in terms of surface accuracy and thin film formation state, so from the viewpoint of avoiding deterioration in image quality, an image forming beam reflecting region that reflects a light beam during image formation Is preferably set at the center of the reflecting surface.

  Therefore, it is conceivable that the detection of the light quantity is performed before the image formation following the detection of the light beam for synchronization control performed immediately before the image formation or in this case. Since it is necessary to secure an area for reflecting the light beam for synchronization control and an area for reflecting the light beam at the time of detecting the amount of light on one side of the image forming beam reflecting area on the reflecting surface, the reflection of the rotating polygon mirror is required. The effective length of the surface increases, leading to an increase in the diameter of the rotary polygon mirror, which is undesirable from the viewpoint of temperature and noise. Furthermore, if the timings of detecting the light amount and detecting the light beam for synchronization control are close to each other, stray light caused by the light beam at the time of detecting the light amount enters the light detection sensor at the time of detecting the light beam for synchronization control. As a result, there are problems such as erroneous detection of the timing of the light beam, or stray light caused by the light beam for synchronization control entering the light detection sensor at the time of detecting the amount of light, leading to erroneous detection of the light amount. Arise.

  The present invention has been devised based on such inventor's knowledge, and its main purpose is to detect the light amount of the laser element and the detection of the light beam for synchronization control with a single light detection sensor. Another object of the present invention is to provide a scanning exposure apparatus and an image forming apparatus provided with the scanning exposure apparatus that are configured to avoid adverse effects due to an increase in the diameter of the rotating polygon mirror and stray light in the combined configuration.

  The present invention includes a light source that generates a light beam, a rotating polygon mirror that deflects the light beam from the light source and scans it on a scanned object, and detects and synchronizes the light amount of the light source that is disposed close to the light source. A light detection sensor for detecting a return beam returned by reflecting the control light beam by the reflection means, a light amount control means for controlling the light amount of the light source based on the light amount detected by the light detection sensor, and Synchronization control means for controlling the scanning timing at the time of image formation based on the return beam detected by the light detection sensor, and the light beam for image formation from the light source on the same reflection surface of the rotary polygon mirror A synchronization control beam reflection region for reflecting the synchronization control light beam from the light source is set on the front side in the rotation direction across the image formation beam reflection region for reflecting the image. The rotation direction rear side of the use beam reflecting region, the light amount detected when a beam reflecting region for reflecting the light beam from the light source is to set the configuration when the amount of light detected.

  According to the present invention, the synchronization control beam reflection region and the light amount detection beam reflection region may be set in the surplus portions on both sides of the image formation beam reflection region set at the center of the reflection surface of the rotary polygon mirror. Thus, since it is not necessary to increase the effective length of the reflecting surface, it is possible to avoid an increase in the diameter of the rotary polygon mirror. In addition, the timing of performing light beam detection and light control for synchronization control is greatly shifted, and the reflection angle of the light beam emitted in each process is greatly different. Therefore, the light beam emitted in each process becomes stray light. Inconveniences that adversely affect each other can be avoided.

  A first invention made to solve the above-described problems is a light source that generates a light beam, a rotating polygon mirror that deflects the light beam from the light source and scans the object to be scanned, and is disposed close to the light source. And a light detection sensor for detecting a light amount of the light source and detecting a return beam returned by reflecting a light beam for synchronization control by a reflecting means, and the light source based on the light amount detected by the light detection sensor. On the same reflecting surface of the rotary polygon mirror, the light amount control means for controlling the light quantity of the rotating polygon mirror, and the synchronous control means for controlling the scanning timing at the time of image formation based on the return beam detected by the light detection sensor A synchronization control beam for reflecting the light beam for synchronization control from the light source on the front side in the rotation direction across the image formation beam reflection region for reflecting the light beam for image formation from the light source With morphism area is set, the rotation direction rear side of the image forming beam reflective region, the light amount detected when a beam reflecting region for reflecting the light beam from the light source is to set the configuration when the amount of light detected.

  According to this, the synchronization control beam reflection area and the light quantity detection beam reflection area may be set in the surplus portions on both sides of the image formation beam reflection area set at the center of the reflection surface of the rotary polygon mirror. Therefore, it is not necessary to increase the effective length of the reflecting surface, so that an increase in the diameter of the rotary polygon mirror can be avoided. In addition, the timing of performing light beam detection and light control for synchronization control is greatly shifted, and the reflection angle of the light beam emitted in each process is greatly different. Therefore, the light beam emitted in each process becomes stray light. Inconveniences that adversely affect each other can be avoided.

  A second invention made to solve the above-mentioned problems is that, in the first invention, the reflecting means is the rotating polygon mirror, and the light beam for synchronization control from the light source is the rotating polygon. The light beam is reflected by the reflecting surface of the mirror, and the reflected beam is incident on the light detection sensor as the return beam.

  According to a third aspect of the present invention for solving the above-mentioned problems, in the first aspect of the present invention, the reflecting means is a synchronous mirror provided separately from the rotary polygon mirror, and is used for synchronous control from the light source. The light beam is incident on the synchronous mirror through the reflecting surface of the rotating polygon mirror, and the reflected beam is incident on the light detection sensor as the return beam through the reflecting surface of the rotating polygon mirror. The configuration.

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

  FIG. 1 is a schematic cross-sectional view showing an image forming apparatus to which the present invention is applied. This image forming apparatus forms an image on a recording sheet (image forming medium) S by an electrophotographic method based on image data input from a host device such as an image reading device or a PC (not shown). 1 is supplied to the image forming unit 1 through the pickup roller 3, the conveying roller 4 and the registration roller 5 to perform image forming processing, and then conveyed to the fixing unit 6. Here, after a fixing process for fixing the toner image on the recording paper S by the action of heat and pressure by the heating roller 7 and the pressure roller 8 is performed, the paper is discharged via the transport roller 9 and the paper discharge roller 10. It is discharged onto the tray 11.

  The image forming unit 1 is a photosensitive drum (scanned body) 13 and an LSU (laser scanning unit, scanning exposure) that forms an electrostatic latent image by irradiating the photosensitive drum 13 with an exposure light beam. Device) 14, a developing device 16 that supplies toner onto the photosensitive drum 13 with a developing roller 15 to develop the electrostatic latent image, and a toner image formed on the photosensitive drum 13 is transferred onto the recording paper S. And a transfer roller 17. In addition, the image forming unit 1 is further provided with a charger for uniformly charging the photosensitive drum 13 and a cleaning unit for cleaning the photosensitive drum 13.

  FIG. 2 is a cross-sectional view of the LSU 14 shown in FIG. The LSU 14 includes a laser block 21 including a laser element that generates a light beam, a rotating polygon mirror 22 that deflects the light beam emitted from the laser block 21 and scans the photosensitive drum 13, and the rotating polygon. It has fθ lenses 23 and 24 for forming an image of the light beam deflected by the mirror 22 on the photosensitive drum 13, and a housing 25 for housing them.

  FIG. 3 is a cross-sectional view of the light source device built in the laser block 21 shown in FIG. The laser block 21 includes a so-called can-type light source device 31. The light source device 31 includes a laser element (light source) 32 that generates a light beam, a heat sink 33 on which the laser element 32 is mounted, and the heat sink. And a cap 35 that surrounds the laser element 32 and the heat sink 33, and a lead pin 36 extending from the stem 34. The cap 35 is provided with an optical glass window 37, and the main beam generated on the front surface of the laser element 32 passes through the optical glass window 37 and is emitted to the outside.

  Further, in the light source device 31, a light receiving element (light detection sensor) 38 is disposed on the stem 34, and a sub-beam for detecting the amount of light generated from the back surface of the laser element 32 is incident on the light receiving element 38. 32 light quantities are detected. Further, as will be described in detail later, the main beam generated from the front surface of the laser element 32 is reflected by a required reflecting means and is returned to the light receiving element 38.

  In addition to the light source device 31, the laser block 21 shown in FIG. 2 includes a collimator lens that converts the light beam emitted from the laser element 32 into parallel light, a cylindrical lens that condenses the light beam in the sub-scanning direction, And an optical system component such as an aperture that shapes the light beam into a predetermined diameter and restricts the incidence of external light.

  FIG. 4 is a block diagram showing a schematic configuration of the control unit of the LSU 14 shown in FIG. The control unit of the LSU 14 includes a laser drive circuit 41, a beam light amount detection circuit 43, a light amount control circuit 44, and a beam timing detection circuit 45.

  The laser drive circuit 41 supplies a laser drive current to the laser element 32 of the light source device 31 to drive the laser element 32, and is an image input from a laser modulation control circuit 47 provided in the control unit on the main body side. The turning on / off of the laser element 32 is controlled in accordance with the signal (nVIDEO). In the laser modulation control circuit 47, modulation is performed by a required method such as pulse width modulation (PWM) or pulse intensity modulation (PAM).

  The beam light amount detection circuit 43 detects a change in intensity of the sub beam for light amount detection generated from the back surface of the laser element 32 based on a monitor signal (Vm) output from the light receiving element 38 of the light source device 31. . The light quantity control circuit 44 obtains a light quantity correction amount by comparing the light quantity indicated by the light quantity detection signal from the beam light quantity detection circuit 43 with a predetermined reference value, and outputs a light quantity control signal corresponding thereto to the laser drive circuit 41. Thus, the amount of light of the laser element 32 that fluctuates according to environmental changes such as temperature can be kept constant.

  Based on the monitor signal (Vm) output from the light receiving element 38, the beam timing detection circuit 45 reflects the main beam generated from the front surface of the laser element 32 by a required reflecting means and returns the returned beam timing. Is detected and the beam timing signal (nHSYNC) is output to the laser modulation control circuit 47. The laser modulation control circuit 47 uses the beam timing signal (nHSYNC) from the beam timing detection circuit 45 as a reference for the laser. A timing signal for defining the drive timing is output to the drive circuit 41 and the light amount control circuit 44, and the laser drive circuit 41 drives the laser element 32 based on the timing signal from the laser modulation control circuit 47 to write one line. Be started. In the beam light amount detection circuit 43, the light amount detection timing is defined by the APC timing signal (nSH) output from the laser modulation control circuit 47.

  FIG. 5 is a perspective view schematically showing a light beam reflection region in the rotary polygon mirror 22 shown in FIG. In the rotary polygon mirror 22, on the same reflecting surface 51, for synchronization control that reflects the light beam for synchronization control on the front side in the rotation direction across the image formation beam reflection region that reflects the light beam for image formation. A beam reflection area is set, and a light beam detection time beam reflection area for reflecting a light beam at the time of light quantity detection is set on the rear side in the rotation direction of the image forming beam reflection area.

  FIG. 6 is a timing chart of each signal shown in FIG. In accordance with an image signal (nVIDEO) for switching on / off of the laser element 32 on the n-plane which is one of the reflecting surfaces 51 of the rotary polygon mirror 22, a light beam for synchronization control is provided before the image forming image signal. The laser element 32 is forcibly lit to generate it, and the laser element 32 is forcibly lit to generate a sub-beam for detecting the amount of light after the image forming image signal. In response to this, the return beam and the sub beam of the main beam emitted by the laser element 32 are received by the light receiving element 38, and the monitor signal (Vm) output from the light receiving element 38 changes.

  At the time of forced lighting for light amount detection, the monitor signal (Vm) output from the light receiving element 38 changes due to the reception of the sub beam, and the light amount specified by the APC timing signal (nSH) in the beam light amount detection circuit 43. The light quantity detection operation is executed within the detection period (APC section). On the other hand, at the time of forced lighting for synchronous control, the monitor signal (Vm) changes due to reception of the return beam of the main beam in addition to the sub beam, and the beam timing detection circuit 45 outputs the monitor signal (Vm) to a predetermined value. The return beam of the main beam is detected by comparing with the threshold value, and a beam timing signal (nHSYNC) is output.

  FIG. 7 is a top view showing a state in which the light beam for synchronization control in the LSU 14 shown in FIG. 2 is reflected. FIG. 8 is a top view showing a state in which a light beam for image formation is reflected in the LSU 14 shown in FIG. FIG. 9 is a top view showing a state in which a light beam is reflected at the time of light amount detection in the LSU 14 shown in FIG.

  At the time of detection of the light beam for synchronization control performed immediately before image formation, the light beam for synchronization control emitted from the laser element 32 of the light source device 31 is reflected by the rotary polygon mirror 22 as shown in FIG. The light beam is reflected from the front end of the surface 51 in the rotational direction, and the light beam detection operation is started from the state shown in FIG. 7A. From the state shown in FIG. The return beam is incident on the light receiving element 38 of the light source device 31, and the timing of the light beam is detected. During this time, the light beam emitted from the laser element 32 of the light source device 31 is used for image formation as shown in FIG. The light is reflected by the synchronization control beam reflection region on the front side in the rotation direction of the beam reflection region.

  At the time of image formation, as shown in FIG. 8, the light beam emitted from the laser element 32 of the light source device 31 is reflected by the central portion of the reflecting surface 51 of the rotary polygon mirror 22 to scan the photosensitive drum 13. At this time, writing is started in the state shown in FIG. 8A based on the scanning timing acquired by detecting the light beam for synchronization control, and is continued until the state shown in FIG. 8B. During this time, the light beam emitted from the laser element 32 of the light source device 31 is reflected by the image forming beam reflecting region set at the center of the reflecting surface 51 as shown in FIG.

  Further, at the time of light amount detection in which the light receiving element 38 detects the light beam for detecting the light amount generated from the back surface of the laser element 32 of the light source device 31, as shown in FIG. 9, the light beam emitted from the front surface of the laser element 32 is Then, the light is reflected from the end of the reflecting surface 51 of the rotary polygon mirror 22 in the rotational direction, and the light quantity detection operation is continued from the state shown in FIG. 9A to the state shown in FIG. 9B. As shown in FIG. 5, the light beam emitted from the laser element 32 of the apparatus 31 is reflected by the beam reflection area at the time of light quantity detection on the rear side in the rotation direction of the image forming beam reflection area. At this time, the light beam reflected by the rotary polygon mirror 22 travels in a direction significantly different from that of the light source device 31, so that the light beam is incident on the light receiving element 38 of the light source device 31 with high intensity even if it becomes stray light. No adverse effects due to stray light can be avoided.

  FIG. 10 is a cross-sectional view showing another example of the LSU 14 shown in FIG. FIG. 11 is a top view showing a state in which the light beam for synchronization control in the LSU 14 shown in FIG. 10 is reflected.

  Here, a synchronization mirror (reflecting means) 91 that reflects a light beam for synchronization control for adjusting the scanning timing of the rotary polygon mirror 22 is provided, and the light beam emitted from the laser element 32 of the light source device 31 is provided. Is incident on the synchronous mirror 91 via the reflecting surface 51 of the rotating polygon mirror 22, and the reflected beam is incident on the light receiving element 38 of the light source device 31 as a return beam via the reflecting surface 51 of the rotating polygon mirror 22. It has become.

  At the time of detecting the light beam for synchronization control performed immediately before the image formation, the light beam detection operation is started from the state shown in FIG. 11A, and the rotating polygon mirror 22 in the state shown in FIG. The return beam from the reflecting surface 51 is incident on the light receiving element 38 of the light source device 31, and the timing of the light beam is detected. During this time, the light beam emitted from the laser element 32 of the light source device 31 is as shown in FIG. Then, the light is reflected by the synchronization control beam reflection region on the front side in the rotation direction of the image formation beam reflection region set at the center of the reflection surface 51.

  Further, at the time of image formation, similarly to the example shown in FIG. 8, the light beam emitted from the laser element 32 of the light source device 31 is reflected by the central portion of the reflecting surface 51 of the rotary polygon mirror 22 to be photosensitive. The body drum 13 is scanned.

  Further, at the time of detecting the light amount, the main beam emitted from the laser element 32 of the light source device 31 is detected at the rear end in the rotational direction of the reflecting surface 51 of the rotary polygon mirror 22 as in the example shown in FIG. At the time of reflection, the light receiving element 38 detects the sub-beam for detecting the amount of light. At this time, the main beam is reflected in a direction significantly different from that of the light source device 31, so that even if the light beam becomes stray light, the intensity is high. As it is, the light does not enter the light receiving element 38 of the light source device 31, and adverse effects due to stray light can be avoided.

  The scanning exposure apparatus according to the present invention and the image forming apparatus equipped with the scanning exposure apparatus have the effect of avoiding the adverse effects due to an increase in the diameter of the rotating polygon mirror and stray light. The present invention is useful as a scanning exposure apparatus that is used for both the purpose of detecting the amount of light and the purpose of detecting a light beam for synchronization control, and an image forming apparatus including the same, such as a printer, a digital copying machine, and a facsimile machine.

Schematic sectional view showing an image forming apparatus to which the present invention is applied Sectional view of the LSU shown in FIG. Sectional drawing of the light source device incorporated in the laser block shown in FIG. The block diagram which shows schematic structure of the control part of LSU shown in FIG. The perspective view which shows typically the light beam reflective area | region in the rotary polygonal mirror shown in FIG. Timing diagram of each signal shown in FIG. The top view which shows the state which reflects the light beam for synchronous control in LSU shown in FIG. FIG. 3 is a top view showing a state in which a light beam for image formation is reflected in the LSU shown in FIG. The top view which shows the state which reflects the light beam at the time of the light quantity detection in LSU shown in FIG. Sectional drawing which shows another example of LSU shown in FIG. The top view which shows the state which reflects the light beam for synchronous control in LSU shown in FIG.

Explanation of symbols

1 Image forming unit 13 Photosensitive drum (scanned body)
14 LSU (scanning exposure equipment)
21 Laser block 22 Rotating polygon mirror 31 Light source device 32 Laser element (light source)
38 Light-receiving element (light detection sensor)
41 Laser drive circuit 47 Laser modulation control circuit (synchronous control means)
43 Light quantity detection circuit 44 Light quantity control circuit (light quantity control means)
45 Beam Timing Detection Circuit 51 Reflecting Surface 91 Synchronous Mirror

Claims (4)

A light source that generates a light beam, a rotating polygon mirror that deflects the light beam from the light source and scans it on the scanned object, and a light for synchronization control that is disposed close to the light source to detect the light amount of the light source. A light detection sensor for detecting a return beam returned by reflecting the beam by a reflection means, a light amount control means for controlling the light amount of the light source based on the light amount detected by the light detection sensor, and the light detection sensor Synchronization control means for controlling the scanning timing during image formation based on the detected return beam,
On the same reflecting surface of the rotary polygon mirror, a light beam for synchronization control from the light source is placed on the front side in the rotation direction across an image forming beam reflection region for reflecting the light beam for image formation from the light source. A beam reflection area for synchronization control to be reflected is set, and a beam reflection area at the time of light amount detection that reflects a light beam from the light source at the time of light amount detection is set on the rear side in the rotation direction of the image formation beam reflection area. A scanning exposure apparatus.   The reflecting means is the rotating polygon mirror, and the light beam for synchronization control from the light source is reflected by the reflecting surface of the rotating polygon mirror, and the reflected beam enters the light detection sensor as the return beam. The scanning exposure apparatus according to claim 1, wherein:   The reflecting means is a synchronous mirror provided separately from the rotary polygon mirror, and a light beam for synchronization control from the light source is incident on the synchronous mirror via a reflection surface of the rotary polygon mirror, 2. The scanning exposure apparatus according to claim 1, wherein the reflected beam is incident on the light detection sensor as the return beam through the reflecting surface of the rotary polygon mirror. An image forming apparatus comprising the scanning exposure apparatus according to claim 1.

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