Optical scanner and image forming apparatus

Abstract

To detect a change over time of a rotary polygon mirror of an optical scanner even during the operation of the device, and improve image quality while preventing image deterioration over time.SOLUTION: An optical scanner comprises: a semiconductor laser unit 1 that emits a light beam; a rotary polygon mirror 4 that deflects the laser light beam L emitted from the semiconductor laser unit 1 and scans the laser light beam in a main scanning direction; a scan lens 7 that guides the laser light beam L scanned by the rotary polygon mirror 4 to a photoconductor drum 8; a BD 6 that is provided on the upstream side of the scan lens 7 in the main scanning direction, and outputs a signal in response to reception of the laser light beam L; a light quantity sensor 16 that is provided on the upstream side of the BD 6 in the main scanning direction, and detects the quantity of the laser light beam L; and a control section 100 that controls the semiconductor laser unit 1 based on the signal output from the BD 6 and the quantity of light detected by the light quantity sensor 16.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical scanning device and an image forming apparatus, for example, an optical scanning device that performs optical writing using a laser beam in an image forming apparatus such as a laser beam printer (LBP), a digital copier, or a digital facsimile (FAX) device. [Background technology]

[0002] The optical scanning device optically modulates a laser beam emitted from a light source in response to an image signal, and deflects and scans the modulated laser beam by, for example, an optical deflector having a rotating polygon mirror. The deflected and scanned laser beam is guided to a beam detector (hereinafter, referred to as BD) in order to control the timing of the scanning start position on the scanned surface. When the BD detects the laser beam, it outputs a signal. For example, the optical scanning device performs optical scanning and records an image in a state where the laser beam is imaged in a spot shape on a photosensitive body by a scanning lens such as an imaging optical system having fθ characteristics. Note that the fθ lens has a lens characteristic (fθ characteristic) that forms an image of a size (f×θ) obtained by multiplying the laser beam by the focal length f of the fθ lens when the laser beam enters at an angle θ. At this time, the optical scanning device writes out an image after a predetermined time based on the signal output from the BD (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6736368 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the case of the conventional technology, there is a possibility that toner, paper powder, dust in the air, etc. may enter the optical box through the gap between the optical box and the lid. In this state, when the rotating polygon mirror is rotated at high speed, dust particles adhere to the ends of each reflecting surface of the rotating polygon mirror. The adhered dust particles reduce the amount of light at the beginning and end of writing in the image area. When the amount of light decreases, the density at the end of the image becomes thin, and uneven density of the image occurs. In addition, when the rotating polygon mirror is rotated at high speed, the coil and electric circuit that rotates the rotating polygon mirror generate heat, and the optical box expands and deforms due to the heat. The deformation of the optical box changes the position and attitude of the optical elements arranged in the optical box, and the scanning position on the scanned surface is shifted from the specified position in the sub-scanning direction (the direction perpendicular to the scanning direction). As a result, the top and bottom margins on the paper surface of the printed matter become wider or narrower than the specified value. However, there is a problem that it is not possible to detect changes over time in performance that affects image quality, such as a decrease in the reflectance of the rotating polygon mirror and a shift in the scanning position on the scanned surface, while the image forming device is operating.

[0005] The present invention has been made under these circumstances, and aims to detect changes over time in the rotating polygon mirror of an optical scanning device even while the device is in operation, and to achieve high image quality while suppressing image degradation over time. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0007] (1) An optical scanning device comprising: a light source which emits a light beam; a rotating polygon mirror which deflects the light beam emitted from the light source and scans it in a main scanning direction; an optical member which guides the light beam scanned by the rotating polygon mirror to an image carrier; an output means which is provided upstream of the optical member in the main scanning direction and outputs a signal in response to receiving the light beam; a detection means which is provided upstream of the output means in the main scanning direction and detects the amount of light of the light beam; and a control means which controls the light source based on the signal output by the output means and the amount of light detected by the detection means.

[0008] (2) An optical scanning device comprising: a light source which emits a light beam; a rotating polygon mirror which deflects the light beam emitted from the light source and scans it in a main scanning direction; a first optical member which guides the light beam scanned by the rotating polygon mirror to an image carrier; a second optical member which is provided upstream of the first optical member in the main scanning direction; an output means which is provided upstream of the first optical member in the main scanning direction and outputs a signal in response to receiving the light beam scanned by the rotating polygon mirror and focused in the main scanning direction by the second optical member; and a control means which controls the light source based on the signal output by the output means, wherein the output means detects a light amount of the light beam which is upstream in the main scanning direction of the light beam focused in the main scanning direction by the second optical member and is not focused in the main scanning direction, and the control means controls the light source based on the light amount of the light beam which is not focused in the main scanning direction.

[0009] (3) An image forming apparatus comprising: an optical scanning device according to (1) or (2); an image carrier on which an electrostatic latent image is formed by the optical scanning device; a developing means for developing the electrostatic latent image formed on the image carrier with a developer to form a developer image; and a transfer means for transferring the developer image to a recording material. Effect of the Invention

[0010] According to the present invention, it is possible to detect changes over time in the rotating polygon mirror of an optical scanning device even during operation of the device, and to achieve high image quality while suppressing deterioration of the image over time. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view illustrating a configuration of an optical scanning device according to a first embodiment of the present invention; [Diagram 2] FIG. 1 is a partial enlarged view showing the configuration in the vicinity of the BD of the optical scanning device according to the first embodiment; FIG. 2 is a partial enlarged view showing the configuration in the vicinity of the light quantity sensor; [Diagram 3]FIG. 1 is a diagram showing the amount of light input to a light amount sensor of the optical scanning device according to the first embodiment; [Figure 4] FIG. 1 is a schematic explanatory diagram showing the reflection positions of light beams on a rotating polygon mirror in the first embodiment; and FIG. 2 is a schematic explanatory diagram showing the positions of dirt on the rotating polygon mirror. [Diagram 5] FIG. 11 is a perspective view illustrating a configuration in the vicinity of the BD of an optical scanning device according to a second embodiment of the present invention; [Figure 6] FIG. 10 is a diagram showing the incidence angle dependence of reflectance of PMMA in Example 2; and FIG. 11 is a perspective explanatory diagram showing a semiconductor laser. [Figure 7] FIG. 11 is a perspective view illustrating a configuration in the vicinity of the BD of an optical scanning device according to a third embodiment. [Figure 8] FIG. 13 is a diagram showing a configuration of an image forming apparatus according to a fourth embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] In the following description, the direction in which the laser light emitted from the optical scanning device scans the photosensitive drum (or the rotation axis direction of the photosensitive drum) is referred to as the main scanning direction, and the direction perpendicular to the main scanning direction (or the rotation direction of the photosensitive drum) is referred to as the sub-scanning direction. EXAMPLES

[0013] <Optical scanning device> An embodiment of an optical scanning device according to the present invention will be specifically described with reference to Fig. 1 to Fig. 3. Fig. 1 is a perspective explanatory diagram showing the configuration of an optical scanning device of Example 1. An optical scanning device 101 shown in Fig. 1 uses a laser beam to perform optical writing on the surface of a photosensitive drum 8, which is an image carrier, in an image forming device such as a laser beam printer (LBP), a digital copier, or a digital facsimile machine. The optical scanning device 101 has a semiconductor laser unit 1, which serves as a light source for emitting a laser beam L (light beam), and an anamorphic collimator lens 2 in which a collimator lens and a cylindrical lens are integrally molded.

[0014] The optical scanning device 101 also has an aperture stop 3 formed of a through hole, and a rotating polygon mirror 4. The rotating polygon mirror 4 has, for example, four reflecting surfaces 12, and deflects the laser beam L to scan in the main scanning direction. The optical scanning device 101 has an optical deflector 5 that rotates the rotating polygon mirror 4 using a motor (not shown) that is a driving source. The optical scanning device 101 has a BD 6 that detects the laser beam L deflected and scanned by the optical deflector 5 in order to determine the writing start position of the laser beam L on the surface of the photosensitive drum 8. The BD 6 is provided upstream of a scanning lens 7 described later in the main scanning direction, and functions as an output unit that outputs a signal in response to receiving the laser beam L. The optical scanning device 101 has a BD lens 14 that is a second optical member having an anamorphic optical surface, and a light amount sensor 16 that detects the light amount of the laser beam L deflected and scanned by the optical deflector 5. The BD lens 14 is provided between the rotating polygon mirror 4 and the BD 6, and guides the laser light beam L scanned by the rotating polygon mirror 4 to the BD 6 without guiding it to the light amount sensor 16. The light amount sensor 16 is provided upstream of the BD 6 in the main scanning direction, and functions as a detection means for detecting the amount of light of the laser light beam L. The light amount sensor 16 detects a decrease in the reflectance of the reflecting surface 12 of the rotating polygon mirror 4 by detecting the amount of light.

[0015] The optical scanning device 101 has a scanning lens 7, which is a first optical member (optical member) having the function of an fθ lens that serves as an imaging means for directing the laser light beam L deflected and scanned by the optical deflector 5 onto the surface of the photosensitive drum 8 and forming an image. The fθ lens has lens characteristics (fθ characteristics) such that when the laser light enters at an angle θ, it forms an image with a size (f×θ) multiplied by the focal length f of the fθ lens. The optical scanning device 101 has an optical box 9 that houses each optical member including the optical deflector 5. The optical box 9 is made of, for example, black resin and is formed by injection molding.

[0016] The laser beam L emitted from the semiconductor laser unit 1 is converted into a substantially parallel beam or a convergent beam in the main scanning direction and into a convergent beam in the sub-scanning direction by the anamorphic collimator lens 2. Next, the laser beam L passes through an aperture stop 3, where the beam width is restricted, and is imaged on a reflecting surface 12 of a rotating polygon mirror 4 in the form of a focal line that extends long in the main scanning direction.

[0017] The laser light beam L imaged on the reflecting surface 12 of the rotating polygon mirror 4 is deflected and scanned by rotating the rotating polygon mirror 4. The laser light beam L reflected by the reflecting surface 12 scans the light amount sensor 16. Thereafter, as the rotating polygon mirror 4 rotates, the laser light beam L enters the BD lens 14 and scans the BD 6 while being focused in the main scanning direction.

[0018] Next, the laser light beam L is incident on a scanning lens 7 that is long in the main scanning direction. The scanning lens 7, which functions as an fθ lens, is designed to focus the laser light beam L to form a spot on the surface of the photosensitive drum 8, and to keep the scanning speed of the spot constant. In order to obtain such fθ lens characteristics, the scanning lens 7 is formed of an aspheric lens.

[0019] The laser beam L is deflected and scanned by the rotation of the rotary polygon mirror 4, and main scanning is performed by the laser beam L on the surface of the photosensitive drum 8, and sub-scanning is performed by rotating the photosensitive drum 8 about the axis of its cylinder. As a result, an electrostatic latent image according to the image information is formed on the surface of the photosensitive drum 8 that is uniformly charged by a charging means (not shown).

[0020] The control unit 100 includes a CPU 100a, a ROM 100b, a RAM 100c, and a timer 100d. The control unit 100 performs various controls according to a program stored in the ROM 100b in advance, while referring to parameters, tables, etc. stored in the ROM 100b and the timer 100d, and using the RAM 100c as a temporary work area. When the laser beam L is incident on the BD 6, the BD 6 outputs a signal to the control unit 100. When the laser beam L is incident on the light quantity sensor 16, the BD 6 outputs a signal according to the incident light quantity to the control unit 100. The control unit 100 can also control the semiconductor laser unit 1 based on the detection result of the BD 6 and the detection result of the light quantity sensor 16. The control unit 100 functions as a control unit that controls the light source based on the signal output by the BD 6 and the light quantity detected by the light quantity sensor 16.

[0021] <bd> 2(a) is a partial enlarged view showing the configuration in the vicinity of the BD 6 of the optical scanning device 101. The optical scanning device 101 has the BD 6, an optical box 9, and a BD lens 14. The BD 6 has a light receiving surface 10. The optical box 9 has a through hole 13.

[0022] The laser beam L reflected by the rotating polygon mirror 4 shown in Fig. 1 passes through the BD lens 14, becomes a beam of light focused in the main scanning direction, and is scanned in the direction of the arrow X in Fig. 2(a) as the rotating polygon mirror 4 rotates in the direction of the arrow A in Fig. 1 (clockwise direction). The laser beam L scanned in the direction of the arrow X in Fig. 2(a) passes through a through hole 13 provided in the optical box 9 and is incident on the light receiving surface 10 of the BD 6. At this time, the control unit 100 detects the beam by the BD 6, and determines the synchronous detection timing of the writing start position in the main scanning direction on the photosensitive drum 8 based on the signal output from the BD 6.

[0023] <Light intensity sensor> Next, the light amount sensor 16, which is a feature of the first embodiment, will be described with reference to Figs. 2(b) to 4. Fig. 2(b) is a partially enlarged view showing the configuration of the light amount sensor 16 and its vicinity in the optical scanning device 101. The optical scanning device 101 has the light amount sensor 16. The light amount sensor 16 has a light receiving surface 17. A through hole 18 is provided in the optical box 9. Fig. 2(b) also shows the laser light beam L reflected by the reflecting surface 12 of the rotating polygon mirror 4 (not shown). The light amount sensor 16 and the through hole 18 are provided upstream of the BD 6 and the through hole 13 in the direction of the arrow X, in other words, in the main scanning direction.

[0024] The laser beam L is scanned in the direction of the arrow X in FIG. 2(b) as the rotating polygon mirror 4 rotates in the direction of the arrow A in FIG. 1. The laser beam L scanned in the direction of the arrow X in FIG. 2(b) passes through a through hole 18 provided in the optical box 9 and scans the light receiving surface 17 of the light amount sensor 16. The laser beam L becomes a focal line extending long in the main scanning direction on the reflecting surface 12 of the rotating polygon mirror 4, and then becomes a beam that is approximately parallel or weakly convergent in the main scanning direction and spreads in the sub-scanning direction. On the light receiving surface 17 of the light amount sensor 16, this laser beam L becomes a beam of elliptical shape Sp with a major axis of about 3 mm and a minor axis of about 1 mm, for example.

[0025] <Method for detecting a decrease in reflectance of a rotating polygon mirror> Here, a method for detecting a decrease in the reflectance of the rotating polygon mirror 4 based on the amount of light incident on the light receiving surface 17 of the light amount sensor 16 will be described. Fig. 3 is a graph showing time on the horizontal axis and the amount of light input of the laser light beam L to the light receiving surface 17 on the vertical axis.

[0026] (When the reflective surface of the rotating polygon mirror is clean) Graph a in FIG. 3 shows the amount of light input to the light receiving surface 17 when the laser light beam L scans the light amount sensor 16 in the direction of the arrow X in FIG. 2(b). In graph a shown in FIG. 3, after the end of the laser light beam L is incident on the light receiving surface 17, as the laser light beam L advances on the light receiving surface 17 in the direction of the arrow X in FIG. 2(b), the amount of light input to the light receiving surface 17 gradually increases. Then, at time t0, it reaches a threshold value R1. Then, after the amount of light input to the light receiving surface 17 reaches a peak, the amount of light input to the light receiving surface 17 gradually decreases and falls below the threshold value R1 at time t1. The threshold value R1 is a value that is arbitrarily set according to the maximum amount of light input to the light receiving surface 17, for example, to about 20% to 50% of the maximum amount of light input.

[0027] The light amount sensor 16 compares the input light amount with a threshold value R1, and while the input light amount is greater than the threshold value R1, it outputs, for example, a rectangular wave signal to the control unit 100. The pulse width of the signal at this time is set to tp1 (=t1-t0). The control unit 100 measures the pulse width tp1 using the timer 100d.

[0028] (When the reflective surface of the rotating polygon mirror becomes dirty) Next, the amount of light incident on the light quantity sensor 16 of the laser light beam L when the reflecting surface 12 of the rotating polyhedron mirror 4 is soiled will be described. Similar to graph a, the amount of input light of the laser light beam L to the light receiving surface 17 when the reflecting surface 12 is soiled is shown as graph b by a dotted line in FIG. 3. When the laser light beam L scanning in the direction of arrow X in FIG. 2(b) scans on the light receiving surface 17, the amount of input light to the light receiving surface 17 gradually increases and reaches the threshold value R1 at time t2 (>t0). After that, after the amount of input light to the light receiving surface 17 reaches the peak, the amount of input light gradually decreases and falls below the threshold value R1 at time t3 (<t1). The pulse width when the amount of input light at this time is compared with the threshold value R1 is tp2 (=t3 - t2). It is assumed that the control unit 100 measures the pulse width tp2 by the timer 100d. The control unit 100 can detect a decrease in the reflectance of the rotating polyhedron mirror 4 by comparing the magnitudes of the pulse width tp1 and the pulse width tp2. For example, the control unit 100 can determine that the degree of soiling of the reflecting surface 12 of the rotating polyhedron mirror 4 is greater as the pulse width tp2 becomes smaller (the difference between tp1 and tp2 is larger) with respect to the pulse width tp1.

[0029] <Reflection position of the laser light beam incident on the light quantity sensor and BD> FIGS. 4(a) and 4(b) are schematic views showing the positions where the laser light beam L incident on the light quantity sensor 16 and the BD6 is reflected by the reflecting surface 12 of the rotating polyhedron mirror 4. FIG. 4(a) shows the position where the laser light beam L incident on the light quantity sensor 16 is reflected by the rotating polyhedron mirror 4. FIG. 4(b) shows the position where the laser light beam L incident on the BD6 is reflected by the rotating polyhedron mirror 4. Also, the angle 15 indicates the angle of the reflecting surface 12 of the rotating polyhedron mirror 4.

[0030] The rotating polyhedron mirror 4 rotates in the direction of arrow A in FIGS. 4(a) and 4(b), and the laser light beam L reflected by the reflecting surface 12 of the rotating polyhedron mirror 4 scans on the sensors in the order of the light quantity sensor 16 and the BD6. The distances between the position where the laser light beam L is reflected by the reflecting surface 12 of the rotating polyhedron mirror 4 and the angle 15 of the rotating polyhedron mirror 4 are represented as distance ca in FIG. 4(a) and distance cb in FIG. 4(b). At this time, ca < cb In other words, the laser beam L received by the light amount sensor 16 is influenced by the end of the reflecting surface 12 of the rotating polygon mirror 4.

[0031] <Relationship between air flow and adhesion of dirt> Figures 4(c) and (d) show the air flow near the rotating polygon mirror 4 as it rotates and the dirt adhering to the reflecting surface 12. Figure 4(c) is a view of the rotating polygon mirror 4 seen from above, and Figure 4(d) is a view of the reflecting surface 12 seen from the front.

[0032] As shown in FIG. 4(c), when the rotating polygon mirror 4 rotates in the direction indicated by the arrow A, an air flow as indicated by W occurs near the corner 15 of the reflecting surface 12. As a result, dust particles in the air adhere to the area Y of FIG. 4(d) near the corner 15 of the reflecting surface 12. If the light amount sensor 16 is located upstream of the BD6 with respect to the scanning direction of the laser light beam L, the laser light beam L reflected from the end of the reflecting surface 12 of the rotating polygon mirror 4 (near the area Y), where the reflectance is likely to decrease, will be incident on the light amount sensor 16. As a result, the decrease in the reflectance of the rotating polygon mirror 4 can be detected more accurately by the light amount sensor 16.

[0033] As described with reference to FIG. 3, when the pulse width tp1 is measured in the initial state (graph a) when the reflective surface 12 is not soiled, the pulse width tp1 is stored in a storage medium (not shown) of the image forming apparatus, for example, RAM 100c. Here, the storage medium may be RAM 100c, and the control unit 100 stores the measured pulse width tp1 in RAM 100c. Thereafter, the control unit 100 measures the pulse width tp2 for each number of printed sheets. The pulse width tp2 may be measured for each number of printed sheets, every time a predetermined time has elapsed, or at another timing.

[0034] Also, it is possible to know in advance by experiments, etc., how the light amount distribution in the main scanning direction on the photosensitive drum 8 deviates from the initial uniform state due to the decrease in reflectance of the rotating polygon mirror 4. The results obtained by experiments, etc. can be used for correcting the light amount by storing the results obtained by experiments, etc. in advance in the ROM 100b. Here, the results obtained by experiments, etc. may be, for example, as follows. They may be associated with the pulse width tp1, the position in the main scanning direction, and the initial light amount at that position, or they may be associated with the pulse width tp2 at a predetermined timing, the position in the main scanning direction, and the light amount at that position and timing, etc. They may also be in the form of a table. The control unit 100 estimates the light amount distribution on the photosensitive drum 8 based on the information stored in the ROM 100b from the measured value of the pulse width tp2, and can change the light amount of the laser beam L during scanning to bring the light amount distribution closer to the initial uniform state. In addition, by measuring the pulse width tp2 and changing the amount of light during scanning, the light amount distribution on the photosensitive drum 8 can be corrected, thereby suppressing the phenomenon in which the density of the printed matter becomes thinner over time.

[0035] <Method for detecting the position of the laser beam L in the sub-scanning direction> Furthermore, if printing is continued continuously, the temperature inside and around the optical scanning device 101 rises, causing deformation of the optical box 9. Due to the deformation of the optical box 9, the attitudes of the semiconductor laser unit 1 and the anamorphic collimator lens 2 change, and the scanning positions of the laser light beam L on the light quantity sensor 16 and the photosensitive drum 8 in the sub-scanning direction change.

[0036] When the passing position of the laser light beam L on the light quantity sensor 16 moves away from the center in the sub-scanning direction, the amount of light entering the light receiving surface 17 decreases, and the pulse width becomes smaller in the same manner as described in Fig. 3. Whether the position in the sub-scanning direction shifts upward or downward when the temperature rises depends on the shape of the optical box 9, and therefore it is possible to grasp this in advance by experiments, etc. Also, by storing the position shift in the sub-scanning direction obtained in advance by experiments, etc. in ROM 100b, it can be used to correct the position shift in the sub-scanning direction.

[0037] To detect the position of the laser beam L in the sub-scanning direction, the control unit 100 first stores the initial pulse width tp1 in, for example, the RAM 100c, in the same manner as in detecting a decrease in the reflectance of the rotating polygon mirror 4. Then, from when the image forming apparatus is turned on until it is turned off, the control unit 100 detects the pulse width tp2, for example, at regular time intervals, and compares the pulse width tp1 with the pulse width tp2. This makes it possible to detect a change in the scanning position on the BD 6 in the sub-scanning direction.

[0038] The scanning position in the sub-scanning direction on the BD 6 correlates with the scanning position in the sub-scanning direction on the photosensitive drum 8. Therefore, by grasping the relational expression in advance, the control unit 100 can estimate the scanning position in the sub-scanning direction on the photosensitive drum 8 from the scanning position in the sub-scanning direction on the BD 6. Based on the estimated scanning position in the sub-scanning direction on the photosensitive drum 8, when the scanning position in the sub-scanning direction is shifted by, for example, half the scanning interval on the surface of the recording material, the control unit 100 may correct the writing timing of the image in the sub-scanning direction by one line. Here, half the scanning interval is, for example, 21.2 μm (=25.4 cm / 600 dpi / 2) when the resolution in the sub-scanning direction is 600 dpi. From the above, by correcting the writing timing of the laser beam L in the sub-scanning direction on the photosensitive drum 8, the influence of the scanning position shift of the laser beam L on the margin shift of the image can be eliminated.

[0039] The light quantity correction is performed based on a long-term change in the pulse width tp2, and the positional deviation in the sub-scanning direction of the laser beam L is detected by detecting a short- to medium-term change in the pulse width tp2 from when the image forming apparatus is turned on to when it is turned off. Therefore, the control unit 100 can perform the light quantity correction and the positional correction in the sub-scanning direction in parallel.

[0040] In the first embodiment, during the operation of the image forming apparatus (in other words, the optical scanning apparatus), the light amount sensor 16 detects a decrease in the reflectance of the reflecting surface 12 of the rotating polygon mirror 4, and corrects the decrease, thereby preventing image degradation. Also, by detecting a positional deviation in the sub-scanning direction on the photosensitive drum 8 and correcting the writing timing in the sub-scanning direction, it is possible to prevent a marginal deviation of the image. That is, the control unit 100 corrects the amount of light of the laser beam L emitted from the light source based on the amount of light detected by the light amount sensor 16. Also, the control unit 100 corrects the deviation of the position (scanning position) scanned by the laser beam L in the sub-scanning direction based on the amount of light detected by the light amount sensor 16. The correction of the amount of light and the correction of the deviation of the scanning position in the sub-scanning direction are the same in the following embodiments.

[0041] As described above, according to the first embodiment, even during operation of the device, it is possible to detect the change over time of the rotating polygon mirror of the optical scanning device, and realize high image quality while suppressing image deterioration over time. That is, with a simple configuration, it is possible to detect the decrease in reflectance of the rotating polygon mirror of the optical scanning device during operation of the image forming device (in other words, the optical scanning device), and to correct it. As a result, it is possible to suppress image deterioration over time, which also contributes to extending the life of the image forming device. In addition, since it is possible to detect the deviation of the scanning position in the sub-scanning direction on the scanned surface with a simple configuration, it is possible to realize high image quality of the output image of the image forming device. EXAMPLES

[0042] <bd> FIG. 5 is a perspective explanatory diagram showing a configuration in the vicinity of the BD 6 of the optical scanning device 102 of the second embodiment. In addition, in the line showing the laser light beam L in FIG. 5, the dashed line portion does not interfere with the BD lens 14 and represents the optical path on the other side of the BD lens 14. The second embodiment differs from the first embodiment in that the optical box 9 has a reflecting surface 21 and the BD 6 also serves as a light amount sensor. Here, the BD 6 has a light receiving surface 10 and is provided upstream of the scanning lens 7 in the main scanning direction. The BD 6 functions as an output means that outputs a signal in response to receiving the laser light beam L input through the BD lens 14 at the light receiving surface 10. In addition, the BD 6 detects the light amount of the laser light beam L input without (without) passing through the BD lens 14 and upstream of the BD lens 14 in the main scanning direction. In the second embodiment, the laser light beam L not passing through the BD lens 14 is input to the light receiving surface 10, and then the laser light beam L passing through the BD lens 14 is input to the light receiving surface 10. That is, the laser beams L are input to the light receiving surface 10 with a time difference. The control unit 100 controls the light source based on the light amount of the laser beams L input to the light receiving surface 10 without passing through the BD lens 14. Note that the same components as those in the first embodiment are denoted by the same reference numerals and descriptions thereof will be omitted.

[0043] When the rotating polygon mirror 4 is in a certain rotation phase, the laser beam L is reflected by the reflecting surface 21 integrated with the optical box 9 and enters the light receiving surface 10 of the BD 6 without passing through lenses including the BD lens 14. That is, the reflecting surface 21 integrated with the optical box 9, which is a reflecting member, reflects the laser beam L scanned by the rotating polygon mirror 4 and guides it to the light receiving surface 10 of the BD 6 without passing through the BD lens 14. Since the laser beam L does not pass through lenses, the shape of the laser beam L when scanning the light receiving surface 10 is an ellipse similar to the ellipse Sp shown in FIG. 2(b). Therefore, the decrease in reflectance of the rotating polygon mirror 4 and the scanning position in the sub-scanning direction can be detected by the same method as the method shown in FIG. 3. That is, even in the second embodiment, the control unit 100 can correct the light amount and the scanning position in the sub-scanning direction based on the pulse widths tp1 and tp2 from the detection result of the BD 6.

[0044] Thereafter, the rotating polygon mirror 4 rotates in the direction of arrow A in Fig. 1, and the laser beam L is scanned in the direction of arrow B in Fig. 5, and enters the BD lens 14. The laser beam L that has passed through the BD lens 14 enters the light receiving surface 10 of the BD 6 in a condensed state. At this time, the beam is detected by the BD 6, and this timing is set as the synchronous detection timing for the writing start position in the main scanning direction.

[0045] Reflective surface 21 is, for example, a mirror with a metal film or a dielectric multilayer film deposited on optical box 9. Reflective surface 21 may also be a highly reflective sheet attached to optical box 9. Reflective surface 21 may also be the surface of optical box 9 itself. However, even if the surface of optical box 9 is used as is, the reflectance of reflective surface 21 needs to be 30% or more for the following reasons.

[0046] The amount of light when optically writing on the surface of the photosensitive drum 8 varies depending on the temperature and humidity environment surrounding the image forming apparatus, the film thickness of the photosensitive drum 8, etc., so the minimum and maximum values ​​of the usable range of the amount of light are Min / Max ≦ 1 / 2 In addition, the light amount sensor may not be able to accurately measure the amount of light when the amount of incident light is 15% or less of the maximum amount of incident light. Min / max x reflectance ≥ 15% Therefore, the reflectance must be 30% or more.

[0047] <Relationship between incident angle and reflectance> FIG. 6(a) shows the incidence angle dependence of reflectance of PMMA (Poly Methyl Methacrylate), a commonly used representative resin. In FIG. 6(a), the horizontal axis shows the incidence angle (°) and the vertical axis shows the reflectance (%). Here, the incidence angle is the angle that the incident light makes with respect to the normal to the reflecting surface 21. The thick solid line shows the incidence angle dependence of the reflectance Rs of S-polarized light, and the thin solid line shows the incidence angle dependence of the reflectance Rp of P-polarized light.

[0048] As described above, in the optical scanning device 102 of the second embodiment, the optical box 9 is made of a resin made of a mixture of various materials in order to increase its strength. Therefore, although Fig. 6(a) is not strictly equivalent to the incidence angle dependency of the reflectance of the optical box 9, it can be considered that it is roughly equivalent. From Fig. 6(a), it can be seen that in order to achieve a reflectance of 30% or more, the incidence angle of the laser light beam L on the reflecting surface 12 needs to be at least 70° or more for S-polarized light and 80° or more for P-polarized light.

[0049] <Output light from semiconductor laser> FIG. 6(b) shows the semiconductor laser 22 contained in the semiconductor laser unit 1 of FIG. 1. The output light of the semiconductor laser 22 is linearly polarized light as shown by the dashed line in FIG. 6(b). The semiconductor laser 22 can be rotated in the direction of the arrow Z. Therefore, by rotating the semiconductor laser 22 as shown by the arrow Z in FIG. 6(b), the ratio of S-polarized light and P-polarized light of the laser light beam L with respect to the reflecting surface 21 can be adjusted. In the second embodiment, the semiconductor laser 22 is rotated so that most of the laser light beam L is reflected as S-polarized light. That is, the semiconductor laser 22 is rotated and adjusted so that the ratio of S-polarized light to P-polarized light of the laser light beam L reflected by the reflecting surface 21 is larger than that of P-polarized light. This makes it possible to ensure a predetermined reflectance even when the reflecting surface 21 is formed by the optical box 9. That is, in the above-mentioned incidence angle dependency, it is not necessary to consider P-polarized light, and the incidence angle should be 70° or more.

[0050] As described above, in the second embodiment, the BD 6 can also function as a light amount sensor, and a simpler configuration can be used to detect the decrease in reflectance of the rotating polygon mirror 4 and the scanning position in the sub-scanning direction while the image forming apparatus is in operation. As described above, according to the second embodiment, even while the apparatus is in operation, it is possible to detect the change over time in the rotating polygon mirror of the optical scanning device, and achieve high image quality while suppressing image deterioration over time. EXAMPLES

[0051] <bd> FIG. 7 is a perspective explanatory diagram showing the configuration near the BD6 of the optical scanning device 103 of the third embodiment. In FIG. 7, the dashed lines represent the optical path passing through the BD lens 14 and the optical path emerging from the BD lens 14 on the other side of the BD lens 14. The third embodiment differs from the second embodiment in that the lens end surface 24, which is a part of the end surface 23 of the BD lens 14 that does not have a lens function, plays the role of the reflecting surface 21 of the second embodiment. That is, the BD lens 14, which is the second optical member, has a first portion that focuses the laser beam L scanned by the rotating polygon mirror 4 in the main scanning direction and makes it incident on the light receiving surface 10 of the BD6. In addition, the BD lens 14 has an end surface 23, which is the second portion that does not focus the laser beam L scanned by the rotating polygon mirror 4 in the main scanning direction and makes it incident on the light receiving surface 10 of the BD6. The same components as those of the first embodiment are given the same reference numerals, and the description thereof will be omitted.

[0052] When the rotating polygon mirror 4 is in a certain rotation phase, the laser beam L is incident on the end 23 of the BD lens 14 that does not have a lens function, is reflected by the inner surface of the lens end face 24 (reflected toward the light receiving surface 10), and passes through the end 23 of the BD lens 14. Since the end 23 is a transparent member that does not have a lens function, the shape of the laser beam L when scanning the light receiving surface 10 becomes an ellipse similar to the ellipse shape Sp shown in FIG. 2(b). Therefore, the decrease in reflectance of the rotating polygon mirror 4 and the scanning position in the sub-scanning direction can be detected by a method similar to the method shown in FIG. 3. That is, in the third embodiment as well, the control unit 100 can correct the light amount and the scanning position in the sub-scanning direction based on the pulse widths tp1 and tp2 from the detection result of the BD 6.

[0053] Thereafter, when the rotating polygon mirror 4 rotates and the laser beam L passes through the BD lens 14, the laser beam L is focused and enters the light receiving surface 10 of the BD 6, similar to the method shown in Fig. 2(a). At this time, the beam is detected by the BD 6, and this timing is set as the synchronous detection timing for the writing start position in the main scanning direction. The lens end surface 24 is, for example, a mirror on which a metal film or a dielectric multilayer film is evaporated onto the end surface of the BD lens 14. The lens end surface 24 may also be a sheet with high reflectivity attached.

[0054] In the third embodiment, the lens end surface 24 having no lens function is provided in the BD lens 14, which allows for freedom in designing the shape around the BD lens 14, making it possible to design a more compact scanning optical device. As described above, according to the third embodiment, even during operation of the device, it is possible to detect changes over time in the rotating polygon mirror of the optical scanning device, and achieve high image quality while suppressing image degradation over time. EXAMPLES

[0055] [Explanation of laser beam printer] FIG. 8 shows a schematic configuration of a laser beam printer as an example of an image forming apparatus. The laser beam printer 1000 (hereinafter, referred to as the printer 1000) includes a photosensitive drum 1010, a charging unit 1020, and a developing unit 1030 as a developing unit. The photosensitive drum 1010 is an image carrier on which an electrostatic latent image is formed, and corresponds to the photosensitive drum 8 in the first to third embodiments. The charging unit 1020 uniformly charges the photosensitive drum 1010. An optical scanning device 1025 as an exposure unit forms an electrostatic latent image by scanning the photosensitive drum 1010 with a laser beam according to image data. The optical scanning device 1025 is illustrated in a simplified form in FIG. 8. The optical scanning device 1025 corresponds to the optical scanning device 101 in the first embodiment, the optical scanning device 102 in the second embodiment, and the optical scanning device 103 in the third embodiment. The developing unit 1030 develops the electrostatic latent image formed on the photosensitive drum 1010 with toner, which is a developer, to form a toner image, which is a developer image.

[0056] A toner image formed on the photosensitive drum 1010 (image carrier) is transferred to a sheet P as a recording material supplied from a cassette 1040 by a transfer unit 1050, which is a transfer means. Then, the unfixed toner image transferred to the sheet P is fixed by a fixing device 1060 and discharged to a tray 1070. The photosensitive drum 1010, the charging unit 1020, the developing unit 1030, and the transfer unit 1050 constitute an image forming unit. The printer 1000 also includes a power supply device 1080, which supplies power to a driving unit such as a motor and a control unit 5000. The control unit 5000 has a CPU (not shown) and controls an image forming operation by the image forming unit, a conveying operation of the sheet P, and the like. The control unit 5000 may correspond to the control unit 100 in the first to third embodiments.

[0057] When the printer 1000 finishes a print operation, after a predetermined time has elapsed, the printer 1000 transitions to a standby state in which the printer can immediately perform a print operation. After a further predetermined time has elapsed, the printer 1000 transitions from the standby state to a sleep state, which is a low power consumption mode, in order to reduce power consumption during standby. The printer 1000 has three states: a sleep state and a standby state, which are second modes, and a print state, which is a first mode, and the control unit 5000 transitions the printer 1000 to each of these states. Note that the image forming apparatus to which the optical scanning devices 101, 102, and 103 of the first to third embodiments can be applied is not limited to the configuration exemplified in FIG. 8.

[0058] As described above, according to the fourth embodiment, even during operation of the device, it is possible to detect the change over time of the rotating polygon mirror of the optical scanning device, and to realize high image quality while suppressing image deterioration over time. [Explanation of symbols]

[0059] 1 Semiconductor laser unit 4 Rotating polygon mirror 6BD 7 Scanning Lens 16 Light sensor 100 Control section< / bd> < / bd> < / bd>

Claims

1. a light source that emits a luminous flux; a rotating polygonal mirror that deflects the light beam emitted from the light source and scans it in a main scanning direction; an optical member that guides the light beam scanned by the rotary polygon mirror to an image carrier; an output unit that is provided upstream of the optical member in the main scanning direction and outputs a signal in response to receiving the light beam; a detection means provided upstream of the output means in the main scanning direction and configured to detect the amount of light of the light beam; a control unit that controls the light source based on the signal output by the output unit and the amount of light detected by the detection unit, An optical scanning device characterized in that the light beam reaching the detection means is reflected at a position closer to the end of the reflecting surface of the rotating polygon mirror in the main scanning direction than the light beam reaching the output means.

2. An optical scanning device as described in claim 1, characterized in that when the optical element is a first optical element, a second optical element is provided between the rotating polygon mirror and the output means, which guides the light beam scanned by the rotating polygon mirror to the output means without guiding it to the detection means.

3. the rotating polygonal mirror has a reflecting surface that reflects the light beam, the detecting means detects the decrease in reflectance of the reflective surface by detecting the amount of light; 2. The optical scanning device according to claim 1, wherein the control means corrects the amount of light emitted from the light source based on the amount of light detected by the detection means.

4. 2. The optical scanning device according to claim 1, wherein the control means corrects a deviation of the scanning position of the light beam in a sub-scanning direction perpendicular to the main scanning direction based on the light amount detected by the detection means.

5. An optical scanning device as described in Claim 1, characterized in that the control means controls the writing start position on the image carrier in the main scanning direction based on the signal output by the output means.

6. a light source that emits a luminous flux; a rotating polygonal mirror that deflects the light beam emitted from the light source and scans it in a main scanning direction; a first optical member that guides the light beam scanned by the rotary polygon mirror to an image carrier; a second optical member provided upstream of the first optical member in the main scanning direction; an output unit that is provided upstream of the first optical member in the main scanning direction and outputs a signal in response to receiving the light beam scanned by the rotary polygon mirror and condensed in the main scanning direction by the second optical member; a control means for controlling the light source based on the signal output by the output means; Equipped with the output means detects the amount of light of the light beam that is located upstream in the main scanning direction of the light beam that is converged in the main scanning direction by the second optical member and is not converged in the main scanning direction; The optical scanning device according to claim 1, wherein the control means controls the light source based on the amount of light of the light beam that is not converged in the main scanning direction.

7. 7. The optical scanning device according to claim 6, further comprising a reflecting member arranged upstream of the second optical member in the main scanning direction, which reflects the light beam scanned by the rotating polygon mirror and guides it to the output means without passing through the second optical member.

8. an optical box that houses the rotary polygon mirror, the first optical member, and the second optical member; 8. The optical scanning device according to claim 7, wherein the reflecting member is provided integrally with the optical box.

9. 9. The optical scanning device according to claim 8, wherein the reflecting member has a reflectance of 30% or more.

10. 10. The optical scanning device according to claim 9, wherein the incident angle of the light beam scanned by the rotary polygon mirror onto the reflecting member is 70 degrees or more.

11. the light source is rotatable around an optical axis; 11. The optical scanning device according to claim 10, wherein the light source is adjusted by rotation about the optical axis so that the proportion of S-polarized light in the light beam reflected by the reflecting member is greater than the proportion of P-polarized light.

12. The optical scanning device of claim 6, characterized in that the second optical element has a first portion that focuses the light beam scanned by the rotating polygon mirror in the main scanning direction and makes it incident on the output means, and a second portion that is located upstream of the first portion in the main scanning direction and makes the light beam scanned by the rotating polygon mirror incident on the output means without focusing it in the main scanning direction.

13. The optical scanning device of claim 6, characterized in that, of the light beams that reach the output means, the light beams that are not focused in the main scanning direction are reflected at a position closer to the end of the reflecting surface of the rotating polygon mirror in the main scanning direction than the light beams that are focused in the main scanning direction by the second optical member.

14. the rotating polygonal mirror has a reflecting surface that reflects the light beam, the output means detects the amount of light of the light beam that is not converged in the main scanning direction, thereby detecting a decrease in the reflectance of the reflecting surface; 7. The optical scanning device according to claim 6, wherein the control means corrects the amount of light emitted from the light source based on the amount of light of the light beam that is not converged in the main scanning direction.

15. The control unit, based on the light amount of the light beam that is not converged in the main scanning direction, 7. The optical scanning device according to claim 6, wherein deviation of the scanning position of the light beam in a sub-scanning direction perpendicular to the main scanning direction is corrected.

16. 7. The optical scanning device according to claim 6, wherein said control means controls a write start position on said image carrier in said main scanning direction based on the signal output by said output means.

17. an optical scanning device according to any one of claims 1 to 16; the image carrier on which an electrostatic latent image is formed by the optical scanning device; a developing means for developing the electrostatic latent image formed on the image carrier with a developer to form a developer image; a transfer means for transferring the developer image onto a recording material; An image forming apparatus comprising:

Images