JP4632981B2 - Manufacturing method of laser beam scanning unit, laser beam scanning unit, image forming apparatus, and adjustment method of laser beam scanning unit - Google Patents

Description

  In the present invention, a laser beam emitted from a plurality of light sources is irradiated to a polygon mirror so that adjacent laser beams form a predetermined angle Δθ in the main scanning direction, and reflected light of each laser beam from the polygon mirror is exposed. The present invention relates to a method for manufacturing a multi-beam type laser beam scanning unit for irradiating a drum, a laser beam scanning unit, an image forming apparatus, and a method for adjusting a laser beam scanning unit. In particular, the present invention relates to a copying machine, a printer, a facsimile machine, an Internet facsimile machine, which is an apparatus for forming an image on recording paper, and a multifunction machine having any one of these functions.

  2. Description of the Related Art Conventionally, image forming apparatuses such as copying machines that form an image on recording paper by an electrophotographic method have been demanded for higher speed and higher image quality. Various proposals have been disclosed for this requirement.

For example, laser beams emitted from a plurality of light sources are irradiated to a polygon mirror so that adjacent laser beams form a predetermined angle Δθ in the main scanning direction, and the reflected light of each laser beam from the polygon mirror is applied to the photosensitive drum. An image forming apparatus having a multi-beam type laser beam scanning unit to be irradiated has been proposed (see Patent Document 1). In such an image forming apparatus, it is possible to improve the resolution (or printing speed) substantially in proportion to the number of light sources.
JP 2003-84222 A

  In such an image forming apparatus, the irradiation position of the reflected light on the photosensitive drum is separated by a distance corresponding to the predetermined angle Δθ in the main scanning direction. Therefore, in order to irradiate the same position in the main scanning direction, a laser beam is used. It is necessary to delay the light emission timing every time.

  However, if the light emission timing is delayed for each laser beam, the latent image formed on the photosensitive drum by the distance obtained by multiplying the delayed time by the rotational speed (peripheral speed) of the photosensitive drum in the sub-scanning direction from the resolution. As a result, the image quality is deteriorated due to separation beyond a predetermined beam pitch to be determined.

  The present invention has been made in view of the above problems, and a method of manufacturing a multi-beam laser beam scanning unit capable of realizing high image quality, a laser beam scanning unit, an image forming apparatus, and a method of adjusting a laser beam scanning unit The purpose is to provide.

  In order to achieve the above object, a method of manufacturing a laser beam scanning unit according to claim 1, wherein a laser beam emitted from a plurality of light sources is converted into a polygon so that adjacent laser beams form a predetermined angle Δθ in the main scanning direction. A method of manufacturing a multi-beam laser beam scanning unit that irradiates a mirror and irradiates the photosensitive drum with reflected light of each laser beam from the polygon mirror, and irradiates the photosensitive drum based on the predetermined angle Δθ. And a position adjusting step of adjusting the position of the reflected light of each laser beam in the sub-scanning direction so that the beam pitch when forming an image on the photosensitive drum is equal.

  The method of manufacturing a laser beam scanning unit according to claim 2 is the method of manufacturing the laser beam scanning unit according to claim 1, wherein, in the position adjustment step, the resolution D in the sub-scanning direction, the surface of the polygon mirror The position of the reflected light in the sub-scanning direction is adjusted based on at least one of the number M and the number N of the plurality of light sources.

A manufacturing method of the laser beam scanning unit according to claim 3 is the manufacturing method of the laser beam scanning unit according to claim 2, wherein, in the position adjusting step, a beam pitch P in the sub-scanning direction on the photosensitive drum. (Mm) is P = 25.4 / D × (1−Δθ × M × N / (4 × π))
here,
D: Resolution in the sub-scanning direction (dpi)
Δθ: angle (rad) formed by adjacent laser beams
M: Number of polygon mirror surfaces N: Number of light sources The position of the reflected light in the sub-scanning direction is adjusted to satisfy:

  The manufacturing method of the laser beam scanning unit according to claim 4 is the manufacturing method of the laser beam scanning unit according to claim 3, wherein in the position adjustment step, the laser beam scanning unit is provided between the plurality of light sources and the polygon mirror. The position of the reflected light in the sub-scanning direction is adjusted by rotating the disposed wedge prism.

  The manufacturing method of the laser beam scanning unit according to claim 5 is the manufacturing method of the laser beam scanning unit according to claim 4, wherein the position adjustment step is performed in the main scanning direction and the sub scanning direction of the reflected light. A detection preparation step in which a position detector for detecting the position is arranged on the image plane, and the polygon mirror is fixed at a predetermined position, and one of the plurality of light sources is caused to emit light, thereby detecting the position. A first detection step of detecting a position in the main scanning direction and a sub-scanning direction by the detector, and causing the other light source adjacent to the first light source to emit light among the plurality of light sources, A second detection step for detecting a position in the scanning direction and a position in the main scanning direction corresponding to the other light source obtained in the second detection step are used as the first light source obtained in the first detection step. It should be matched with the corresponding position in the main scanning direction. A mirror rotation step of rotating the polygon mirror, a third detection step of causing the other light source to emit light after the mirror rotation step, and detecting a position in the sub-scanning direction by the position detector; An interval between a position in the sub-scanning direction corresponding to the other light source obtained in the detection step and a position in the sub-scanning direction corresponding to the one light source obtained in the first detection step is defined as the beam pitch P. The adjustment step of rotating the wedge prism disposed between the other light source and the polygon mirror is preferably included.

  A method of manufacturing a laser beam scanning unit according to a sixth aspect is the image forming apparatus according to the fifth aspect, wherein the position detector includes a CCD.

  The manufacturing method of the laser beam scanning unit according to claim 7 is the manufacturing method of the laser beam scanning unit according to claim 5 or 6, wherein the predetermined position is in the main scanning direction of the reflected light. It is characterized in that the position is a position approximately at the center of the scanning range in the main scanning direction.

  The laser beam scanning unit according to claim 8 irradiates a laser beam emitted from a plurality of light sources onto a polygon mirror so that adjacent laser beams form a predetermined angle Δθ with each other in the main scanning direction. A multi-beam type laser beam scanning unit for irradiating the photosensitive drum with reflected light of each laser beam, which is manufactured by the manufacturing method according to claim 1.

  An image forming apparatus according to a ninth aspect includes the laser beam scanning unit according to the eighth aspect, and a photosensitive drum that is irradiated with the laser beam from the laser beam scanning unit to form an image. It is said.

  The laser beam scanning unit according to claim 10 irradiates a laser beam emitted from a plurality of light sources onto a polygon mirror so that adjacent laser beams form a predetermined angle Δθ in the main scanning direction. This is a multi-beam type laser beam scanning unit for irradiating the photosensitive drum with the reflected light of each laser beam, and the beam pitch when forming an image on the photosensitive drum is substantially equal.

  The method of adjusting a laser beam scanning unit according to claim 11, wherein the polygon mirror is irradiated with laser beams emitted from a plurality of light sources so that adjacent laser beams form a predetermined angle Δθ with each other in the main scanning direction. A method of adjusting a multi-beam type laser beam scanning unit that irradiates a photosensitive drum with reflected light of each laser beam on a mirror, and reflects each laser beam irradiated on the photosensitive drum based on the predetermined angle Δθ. The position of the light in the sub-scanning direction is adjusted so that the beam pitch when forming an image on the photosensitive drum is equal.

  According to the method for manufacturing a laser beam scanning unit according to claim 1, in the position adjustment step, the position in the sub-scanning direction of the reflected light of each laser beam irradiated on the photosensitive drum is determined based on the predetermined angle Δθ. Since the beam pitch when forming an image on the drum is adjusted to be equal intervals, it is possible to prevent deterioration in image quality due to the adjacent laser beams being irradiated to the polygon mirror at a predetermined angle Δθ. Can do.

  That is, as the adjacent laser beams are irradiated onto the polygon mirror at a predetermined angle Δθ in the main scanning direction, the latent image formed on the photosensitive drum is separated by a distance corresponding to the predetermined angle Δθ in the sub-scanning direction. However, in the position adjustment process, the position of the reflected light of the laser beam in the sub-scanning direction is adjusted so that the beam pitch when forming an image on the photosensitive drum is equal. Thus, the occurrence of displacement of the latent image in the sub-scanning direction is prevented.

  According to the method of manufacturing a laser beam scanning unit according to claim 2, in the position adjustment step, based on at least one of the resolution D in the sub-scanning direction, the number M of polygon mirror surfaces, and the number N of light sources. As a result, the position of the reflected light in the sub-scanning direction is adjusted, so that more accurate position adjustment is possible and image quality deterioration can be further prevented.

According to the method for manufacturing a laser beam scanning unit according to claim 3, in the position adjustment step, the beam pitch P (mm) in the sub-scanning direction on the photosensitive drum is P = 25.4 / D × (1−Δθ × M × N / (4 × π))
here,
D: Resolution in the sub-scanning direction (dpi)
Δθ: angle (rad) formed by adjacent laser beams
M: Number of polygon mirror surfaces N: Since the position of the reflected light in the sub-scanning direction is adjusted to satisfy the number of light sources, the position of the reflected light in the sub-scanning direction should be adjusted to match the beam pitch P calculated in advance. Therefore, it can be adjusted easily and accurately.

  According to the method of manufacturing a laser beam scanning unit according to claim 4, in the position adjustment step, the wedge prism disposed between the plurality of light sources and the polygon mirror is rotated to thereby rotate the reflected light in the sub-scanning direction. Therefore, the position can be adjusted easily and accurately.

  According to the method of manufacturing a laser beam scanning unit according to claim 5, first, in the detection preparation step, a position detector for detecting the positions of the reflected light in the main scanning direction and the sub scanning direction is disposed on the image plane. The In the first detection step, the polygon mirror is fixed at a predetermined position, one of the plurality of light sources is emitted, and the positions of the main scanning direction and the sub-scanning direction are detected by the position detector. The Next, in the second detection step, among the plurality of light sources, another light source adjacent to one light source emits light, and the position detector detects the position in the main scanning direction. In the mirror rotation step, the second light source is detected. The polygon mirror is rotated so that the position in the main scanning direction corresponding to another light source obtained in the detection step matches the position in the main scanning direction corresponding to one light source obtained in the first detection step. Next, in the third detection step, after the mirror rotation step, another light source is caused to emit light, and the position in the sub-scanning direction is detected by the position detector. In the adjustment step, the distance between the position in the sub-scanning direction corresponding to another light source obtained in the third detection step and the position in the sub-scanning direction corresponding to one light source obtained in the first detection step is The wedge prism disposed between the other light source and the polygon mirror is rotated so as to obtain the beam pitch P.

  Thus, the position in the sub-scanning direction of the reflected light corresponding to one light source and the position in the sub-scanning direction of the reflected light corresponding to another light source adjacent to the one light source at the same position in the main scanning direction. Is adjusted so as to be the beam pitch P, and can be adjusted more accurately.

  According to the method for manufacturing the laser beam scanning unit according to claim 6, since the position detector has the CCD, the position can be accurately detected and the position detector can be manufactured at low cost. Become.

  According to the method of manufacturing a laser beam scanning unit according to claim 7, in the adjustment step, the position of the polygon mirror (= predetermined position) where the position of the reflected light in the sub-scanning direction is adjusted is the main scanning of the reflected light. Since the position in the direction is approximately the center of the scanning range in the main scanning direction, higher image quality can be realized.

  Since the laser beam scanning unit according to the eighth aspect is manufactured by the manufacturing method according to any one of the first to seventh aspects, adjacent laser beams are irradiated to the polygon mirror at a predetermined angle Δθ. Accordingly, it is possible to realize a laser beam scanning unit capable of preventing the image quality deterioration accompanying the above.

  According to the image forming apparatus of the ninth aspect, since the laser beam from the laser beam scanning unit according to the eighth aspect is irradiated and an image is formed on the photosensitive drum, the adjacent laser beam is main-scanned. It is possible to realize an image forming apparatus capable of preventing image quality deterioration caused by irradiating the polygon mirror with a predetermined angle Δθ in the direction.

  According to the laser beam scanning unit of the tenth aspect, since the beam pitch when forming an image on the photosensitive drum is substantially equal, adjacent laser beams form a predetermined angle Δθ with each other in the main scanning direction. It is possible to prevent deterioration in image quality due to irradiation of the polygon mirror.

  According to the adjustment method of the laser beam scanning unit according to claim 11, the position of the reflected light of each laser beam irradiated on the photosensitive drum in the sub-scanning direction is based on the predetermined angle Δθ so that an image is formed on the photosensitive drum. Since the beam pitch at the time of formation is adjusted to be equal intervals, it is possible to prevent deterioration in image quality due to adjacent laser beams irradiating the polygon mirror at a predetermined angle Δθ in the main scanning direction. it can.

  Hereinafter, an example of an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an example of a schematic configuration of an image forming apparatus according to the present invention. Here, the case where the image forming apparatus is a printer will be described. However, the image forming apparatus may be another image forming apparatus (for example, a facsimile, an internet facsimile, a copying machine, a multifunction machine, etc.) that forms an image on recording paper. Good. As shown in FIG. 1, the printer 1 includes a control unit 11, a display unit 12, an operation unit 13, and a print processing unit 14. The printer 1 is communicably connected to a personal computer (not shown), and receives an instruction from the personal computer and forms an image on recording paper.

  The control unit 11 controls the overall operation of the printer 1, and includes a CPU (Central Processing Unit) 111 and a RAM (Random Access Memory) 112.

  The display unit 12 includes an LCD (Liquid Crystal Display), an LED (Light Emitting Diode), and the like, and displays setting information, guidance information, message information, and the like so as to be visible to the user based on instructions from the control unit 11 (CPU 111). To do.

  The operation unit 13 receives an operation input from the user, generates operation input information corresponding to the received operation input, and outputs the operation input information to the control unit 11 (CPU 111). The operation unit 13 includes, for example, various buttons such as a numeric keypad and a start button, and a touch panel formed integrally with the LCD disposed in the display unit 12.

The print processing unit 14 forms an image (here, an image corresponding to image information received from a personal computer) in an electrophotographic manner on a recording sheet, and includes the laser beam scanning unit 2 and the developing unit according to the present invention. 141 and a photosensitive unit 142. The laser beam scanning unit 2 forms an electrostatic latent image on the surface of the photosensitive drum 142a with a laser beam. The developing unit 141 forms a toner image by attaching toner to the electrostatic latent image formed by the laser beam scanning unit 2. Photosensitive unit 142 includes a photosensitive drum 142a, first, the surface of the photosensitive drum 142a is substantially uniformly charged by the charging roller, then the laser beam scanning unit 2, an electrostatic latent image is formed, the developing unit 1 4 1, toner is attached to form a toner image.

  FIG. 2 is a block diagram showing an example of the laser beam scanning unit 2 according to the present invention. The laser beam scanning unit 2 includes a first light source 211, a second light source 212, coupling lenses 221 and 222, a prism 25, a cylinder lens 26, a polygon mirror 27, and an fθ lens 28. The first light source 211 includes, for example, a laser diode and irradiates laser light having a predetermined wavelength toward the polygon mirror 27. The second light source 212 includes a laser diode, for example, and irradiates the polygon mirror 27 with laser light having the same wavelength as that of the first light source 211. Here, the first light source 211, the laser beam from the first light source 211 and the laser beam from the second light source 212 are incident on the polygon mirror 27 at a predetermined angle Δθ in the main scanning direction. A second light source 212 and the like are provided.

  The coupling lenses 221 and 222 respectively convert the laser beams radiating from the first light source 211 and the second light source 212 into substantially parallel rays. The cylinder lens 26 is disposed between the coupling lenses 221 and 222 and the polygon mirror 27, and the laser beams from the first light source 211 and the second light source 212 are respectively positioned at the same position on the reflection surface of the polygon mirror 27. For example, it is converged to (e.g., approximately the center position on one reflecting surface of the polygon mirror 27). The prism 25 changes the optical path of the laser beam from the first light source 211.

The polygon mirror 27 is a polygonal (here, pentagonal) prismatic mirror having a predetermined speed (here, the number of revolutions R (rpm) around the central axis in the direction perpendicular to the paper surface of FIG. )) To rotate. This ensures that reflects the laser beam from the first light source 211 and the second light source 212, through the fθ lens 28, is intended to be scanned in the main scanning direction on the photosensitive drum 142a.

  The fθ lens 28 sets the scanning speed (= moving speed) in the main scanning direction on the photosensitive drum 142 a of the laser beams from the first light source 211 and the second light source 212 reflected by the polygon mirror 27 to a constant speed. . That is, when the laser beam from the first light source 211 and the second light source 212 reflected by the polygon mirror 27 is irradiated on the photosensitive drum 142a without passing through the fθ lens 28, the photosensitive drum 142a of these laser beams is irradiated. The scanning speed in the main scanning direction is lower as it is closer to the center of the photosensitive drum 142a and faster as it is closer to both ends. As a result, an image formed on the photosensitive drum 142a (hereinafter referred to as “on the image surface”) is distorted. Therefore, the fθ lens 28 is disposed to suppress this.

  In addition, coupling lenses 221 and 222, flat glass plates 231 and 232, and wedge prisms 241 and 242 are sequentially disposed between the light sources 211 and 212 and the cylinder lens 26, respectively. A prism 25 is disposed between the lens 26.

  The wedge prisms 241 and 242 adjust the position in the sub-scanning direction on the photosensitive drum 142a of the reflected light from the polygon mirror 27 with respect to the laser beams LB1 and LB2 from the first light source 211 and the second light source 212, respectively. . The wedge prisms 241 and 242 are configured to be rotatable about the principal axis of the prism, and can change the angle formed by the incident light with respect to the incident light by rotating. That is, by rotating the wedge prisms 241 and 242 in a predetermined direction (for example, clockwise), the reflected light of the laser beams LB1 and LB2 from the first light source 211 and the second light source 212, respectively, on the photosensitive drum 142a. The laser beams from the first light source 211 and the second light source 212 are moved by moving the position in the scanning direction in the direction of the paper surface of FIG. 2 and rotating the wedge prisms 241 and 242 in the reverse direction (for example, counterclockwise), respectively. The position in the sub-scanning direction on the photosensitive drum 142a of the reflected light of LB1 and LB2 can be moved in the rear surface direction of FIG.

  The prism 25 causes the laser beam LB1 from the first light source 211 to enter the polygon mirror 27 at a predetermined angle Δθ with respect to the laser beam LB2 from the second light source 212. The optical path is changed.

Next, image quality degradation caused by the laser beam from the first light source 211 and the laser beam from the second light source 212 entering the polygon mirror 27 at a predetermined angle Δθ in the main scanning direction will be described. . As described above, when the laser beam from the first light source 211 and the laser beam from the second light source 212 are incident on the polygon mirror 25 at a predetermined angle Δθ (rad), The separation distance L (mm) in the main scanning direction of both beam spot positions (see FIG. 2; hereinafter, for convenience, the “beam pitch L in the main scanning direction”) is the focal length f (mm) of the fθ lens 28 in the main scanning direction. ) Is given by the following equation (1).
L = f × Δθ (1)

The beam pitch Lv (mm) in the sub-scanning direction is given by the following equation (2) when the resolution is D (dpi).
Lv = 25.4 / D (2)
That is, on the image plane, a desired resolution can be obtained by matching with the beam pitch given by equation (2).

  By the way, since both beam spot positions on the image plane of the laser beams from the first light source 211 and the second light source 212 are separated by a distance L in the main scanning direction, the same position in the main scanning direction on the image plane. In the case of writing to the light source, it is necessary to shift the light emission timings of the first light source 211 and the second light source 212. That is, the light emission timing of the second light source 212 needs to be delayed by a predetermined time with respect to the first light source 211.

Here, as described above, the amount of deviation of the beam pitch in the sub-scanning direction accompanying the delay of the light emission timing of the second light source 212 with respect to the first light source 211 by a predetermined time is obtained. First, the rotational speed R (rpm) of the polygon mirror 27 is the rotational speed (peripheral speed) Vp (mm / sec) of the photosensitive drum 142a, the resolution D (dpi), and the number of faces M of the polygon mirror 27 (example shown in FIG. 2). Then, using M = 5) and the number of light sources N (N = 2 in the example shown in FIG. 2), the following equation (3) is given.
R = Vp × D × 60 / (25.4 × M × N) (3)

Next, the main scanning direction position y of the laser beam transmitted through the fθ lens 28 on the image plane is expressed by the following (4) using the focal length f (mm) of the fθ lens 28 and the scanning angle θ (rad). ).
y = f × θ (4)
Therefore, by differentiating the equation (4) with respect to time, the velocity Vs (mm / sec) of the laser beam on the image plane in the main scanning direction is given by the following equation (5).
Vs = dy / dt = f × dθ / dt (5)

On the other hand, the angular velocity of the polygon mirror 27 is given by the following equation (6) using the rotational speed R (rpm) of the polygon mirror 27.
dφ / dt = 2πR / 60 (6)
Further, there is a relationship of the following expression (7) between the scanning angle θ and the rotation angle φ (rad) of the polygon mirror 27.
θ = 2 × φ (7)
Accordingly, the velocity Vs (mm / sec) of the laser beam in the main scanning direction is given by the following equation (8) by substituting the equations (6) and (7) into the equation (5).
Vs = 4πfR / 60 (8)
Furthermore, the following equation (9) is obtained by substituting equation (3) into equation (8).
Vs = 4π × f × Vp × D / (25.4 × M × N) (9)

Therefore, when the beam pitch in the main scanning direction on the image plane is L (mm) as described above, the delay time ΔT of the light emission timing of the second light source 212 with the first light source 211 as a reference. (Sec) can be obtained by the following equation (10) using the above equation (9).
ΔT = L / Vs = 25.4 × L × M × N / (4π × f × D × Vp) (10)
Therefore, the deviation amount ΔLv (mm) of the beam pitch in the sub-scanning direction is given by the following equation (11) from the equation (10).
ΔLv = ΔT × Vp = 25.4 × L × M × N / (4π × f × D) (11)
Further, by substituting the expression (1) into the expression (11), the deviation ΔLv (mm) of the beam pitch in the sub-scanning direction is given by the following expression (12).
ΔLv = 25.4 × Δθ × M × N / (4π × D) (12)

  Even when the beam pitch in the sub-scanning direction in the stationary state is adjusted to the original value (= 25.4 / D (mm)), as can be seen from the equation (12), the polygon mirror 27 If the angle Δθ or the like of a plurality of incident (here 2) laser beams is not an appropriate value, a deviation occurs by a deviation amount ΔLv (mm) of the beam pitch in the sub-scanning direction. As will be described later using 4, image degradation such as jitter occurs.

The present invention sets the beam pitch P in the sub-scanning direction in a stationary state from the original value (= 25.4 / D (mm)) by the amount of deviation ΔLv (mm) given by the above equation (12). The beam pitch P0 (given by the following equation (13)) that is intentionally shifted in the opposite direction (in the direction in which the beam pitch P narrows) is adjusted (that is, the beam pitch when forming an image on the photosensitive drum 142a). Is adjusted so as to be equal intervals), image deterioration such as jitter is prevented.
P0 = 25.4 / D × (1−Δθ × M × N / (4 × π)) (13)

  FIG. 3 is a pattern diagram showing an example of a dot pattern for inspecting the occurrence of jitter. In the dot pattern shown in FIG. 3, the dot pattern has a period of 3 dots and the beam pitch has a period of 2 dots. Therefore, jitter occurs at a period of 6 dots, which is the least common multiple of both.

  FIG. 4 is a graph showing an example of the occurrence of jitter. Here, for example, the angle Δθ = 8 × π / 180 (rad) (= 8 °) of the laser beam, the number M of faces of the polygon mirror 27, the number of light sources N = 2, and the resolution D = 600 (dpi). In this case, the occurrence of jitter is shown. In this case, the deviation amount ΔLv of the beam pitch in the sub-scanning direction is 0.0075 mm (= 7.5 μm) from the equation (12). At a resolution of 600 dpi, since one dot is 42.3 μm (= 25.4 / 600), a deviation of about 0.18 dots occurs. In this example, when the present invention is applied, P0 = 34.8 μm (= 42.3−7.5) from the equation (13).

  FIG. 4 shows the spatial frequency distribution, in which the horizontal axis indicates the spatial frequency (cycle / mm) and the vertical axis indicates the concentration amplitude intensity. (A) is an overall view, and (b) is an enlargement of the vicinity of a spatial frequency of 4 cycles / mm. As shown in the figure, there is a peak of a 6-dot period that occurs when the beam pitch shift described with reference to FIG. 3 occurs. That is, when the 6-dot interval is expressed in terms of spatial frequency, it is 3.94 (cycle / mm) (= 1000 / (42.3 × 6)), and it can be seen that a peak of density amplitude intensity stands in the vicinity thereof. This is visually detected as jitter in the printed image.

  FIG. 5 and FIG. 6 are flowcharts showing an example of the procedure of the position adjustment process performed when the laser beam scanning unit 2 according to the present invention is manufactured. Here, a case where adjustment is performed manually (by an operator who adjusts the laser beam scanning unit 2) will be described. First, a position detector 3 including a CCD or the like capable of detecting the main scanning direction position and the sub-scanning direction position of the laser beam that has reached the image plane in FIG. 2 is disposed (S101: corresponding to a detection preparation step). . Then, the first light source 211 is turned “ON” (S103). Next, the position in the main scanning direction of the laser beam reaching from the first light source 211 is detected via the position detector 3 (S105: corresponding to part of the first detection step). Then, it is determined whether or not the position in the main scanning direction detected in step 105 is the center position of the scanning range in the main scanning direction (S107).

If it is determined that the position is not the center position (NO in S107), the polygon mirror 27 is rotated so that the main scanning direction position of the laser beam reaching from the first light source 211 is set to the center position of the scanning range (S109: corresponding to as mirror rotation Engineering), the processing is returned to step 105, and the processes after step 105 are repeated. If it is determined that the position is the center position (YES in S107), the position in the sub-scanning direction of the laser beam that has arrived from the first light source 211 is detected via the position detector 3 (S111: first detection step). Equivalent to some). Then, the first light source 211 is turned “OFF” (S113).

  Next, as shown in FIG. 6, the second light source 212 is turned “ON” (S115). Next, the position in the main scanning direction of the laser beam that has arrived from the second light source 212 is detected via the position detector 3 (S117: corresponding to the second detection step). Then, it is determined whether or not the position in the main scanning direction detected in step 117 is the center position of the scanning range in the main scanning direction (S119).

  If it is determined that the position is not the center position (NO in S119), the polygon mirror 27 is rotated so that the position in the main scanning direction of the laser beam reaching from the second light source 212 is the center position of the scanning range (S121: The process is returned to step 117, and the processes after step 117 are repeated. If it is determined that the position is the center position (YES in S119), the position in the sub-scanning direction of the laser beam that has arrived from the second light source 212 is detected via the position detector 3 (S123: in the third detection step). Equivalent to).

  The beam is the distance between the position in the sub-scanning direction of the laser beam reached from the first light source 211 detected in step 111 and the position in the sub-scanning direction of the laser beam reached from the second light source 212 detected in step 123. The pitch P is obtained (S125). Next, whether or not the absolute value of the difference between the beam pitch P obtained in step 125 and the preset beam pitch P0 (given by the above equation (13)) is equal to or less than a threshold value ΔP (for example, 1 μm). Is determined (S127). If it is determined that it is not less than or equal to the threshold value ΔP (= more than the threshold value ΔP) (NO in S127), the wedge prism 242 is rotated in a direction in which the beam pitch P approaches the beam pitch P0 (S129: equivalent to the adjustment step). The process is returned to step 123, and the processes after step S123 are repeated. If it is determined that the value is equal to or less than the threshold value ΔP (YES in S127), the process is terminated.

FIG. 7 is a graph showing an example of a situation of occurrence of jitter after the position adjustment in the flowcharts shown in FIGS. 5 and 6 (when jitter does not occur). FIG. 7 shows the spatial frequency distribution, in which the horizontal axis represents the spatial frequency (cycle / mm) and the vertical axis represents the concentration amplitude intensity. (A) is an overall view, and (b) is an enlargement of the vicinity of a spatial frequency of 4 cycles / mm. As shown in the figure, the peak of the 6-dot period that occurs when the beam pitch shift described with reference to FIG. 3 does not occur. That is, when the 6-dot interval is expressed by a spatial frequency, it is 3.94 (cycle / mm) (= 1000 / (42.3 × 6)), and the peak of the density amplitude intensity that is noticeable in FIG. It turns out that is not seen. This means that the printed image is not visually detected as jitter.

  In this way, when entering the polygon mirror 27, the photosensitive drum 142a is irradiated based on the predetermined angle Δθ which is an angle formed by the laser beam from the first light source 211 and the laser beam from the second light source 212. The position of the reflected light of each laser beam in the sub-scanning direction is adjusted so that the beam pitch when forming an image on the photosensitive drum 142a is equal, so that adjacent laser beams form a predetermined angle Δθ with each other. Therefore, it is possible to prevent the deterioration of image quality (occurrence of jitter, etc.) accompanying the irradiation of the polygon mirror 27.

  That is, as the adjacent laser beams are irradiated onto the polygon mirror 27 at a predetermined angle Δθ, the latent image formed on the photosensitive drum 142a is separated by a distance corresponding to the predetermined angle Δθ in the sub-scanning direction. Although the image quality is deteriorated, the position of the reflected light of the laser beam in the sub-scanning direction is adjusted so that the beam pitch at the time of forming an image on the photosensitive drum 142a is evenly spaced. The occurrence of deviation in the direction is prevented.

  Specifically, it is necessary to adjust the beam pitch deviation amount to be ¼ dot (0.25 dot) or less. However, changes in the environmental conditions such as temperature and humidity affect the refractive index fluctuation of the optical element and the wavelength fluctuation of the laser diode, and also the displacement of the optical element due to the thermal expansion of the optical element itself and its fixing member. The beam pitch varies in the sub-scanning direction by about 0.15 dots. Therefore, the amount of deviation ΔLv of the beam pitch in the sub-scanning direction during adjustment needs to be 0.10 dots or less.

  Further, since the position of the reflected light in the sub-scanning direction is adjusted based on at least one of the resolution D in the sub-scanning direction, the number M of surfaces of the polygon mirror 27, and the number N of light sources, it is more accurate. Position adjustment is possible, and image quality deterioration can be further prevented.

In addition, the beam pitch P (mm) in the sub-scanning direction on the photosensitive drum 142a is P = 25.4 / D × (1−Δθ × M × N / (4 × π)) (14)
here,
D: Resolution in the sub-scanning direction (dpi)
Δθ: angle (rad) formed by adjacent laser beams
M: Number of polygon mirror surfaces N: Since the position of the reflected light in the sub-scanning direction is adjusted to satisfy the number of light sources, the position of the reflected light in the sub-scanning direction should be adjusted to match the beam pitch P calculated in advance. Therefore, it can be adjusted easily and accurately.

  Further, by rotating the wedge prism 242 disposed between the plurality of light sources and the polygon mirror 27, the position of the reflected light in the sub-scanning direction is adjusted, so that the adjustment can be made more easily and accurately. can do.

  Furthermore, the distance between the position in the sub-scanning direction of the reflected light corresponding to one light source and the position in the sub-scanning direction of the reflected light corresponding to another light source adjacent to the one light source at the same position in the main scanning direction. Is adjusted to be the beam pitch P, it is possible to adjust more accurately.

  In addition, since the position detector 3 has a CCD, the position can be accurately detected, and the position detector 3 can be manufactured at low cost.

  Further, the position (= predetermined position) of the polygon mirror 27 where the position of the reflected light in the sub-scanning direction is adjusted is a position where the position of the reflected light in the main scanning direction is approximately the center of the scanning range in the main scanning direction. Therefore, it is possible to achieve higher image quality.

The present invention can also be applied to the following forms.
(A) In this embodiment, the case where the adjustment of the laser beam scanning unit 2 according to the present invention is manually performed has been described. However, a part (or all) of the adjustment may be performed by the control unit 11. In this case, the adjustment is performed more accurately and easily.

  (C) In the present embodiment, the adjustment of the position of the laser beam in the sub-scanning direction has been described using the wedge prism 242. However, the embodiment may be performed using another instrument that changes the traveling direction of the laser beam. .

  (D) In the present embodiment, the case where the position detector detects the position of the laser beam using the CCD has been described. However, the embodiment is performed using another imaging device (such as a complementary metal oxide semiconductor (CMOS) image sensor). But you can.

  (E) In the present embodiment, the case where the position adjustment process shown in FIGS. 5 and 6 is performed at the time of manufacturing the laser beam scanning unit 2 has been described, but it may be used at other timings. For example, when image quality degradation such as jitter occurs for some reason, the laser beam scanning unit 2 may be adjusted.

FIG. 1 is a block diagram showing an example of a schematic configuration of an image forming apparatus according to the present invention. These are the block diagrams which show an example of the laser beam scanning unit which concerns on this invention. These are pattern diagrams showing an example of a dot pattern for inspecting the occurrence of jitter. These are graphs showing an example of the occurrence of jitter (when jitter occurs). These are flowcharts (first half) which show an example of the adjustment procedure of the laser beam scanning unit which concerns on this invention. These are the flowcharts (latter half) which show an example of the adjustment procedure of the laser beam scanning unit which concerns on this invention. These are graphs showing an example of the occurrence of jitter (when no jitter occurs).

Explanation of symbols

1 Printer 11 Control Unit 111 CPU
112 RAM
DESCRIPTION OF SYMBOLS 14 Print processing part 141 Developing unit 142 Photosensitive unit 142a Photosensitive drum 2 Laser beam scanning unit 211, 212 1st light source, 2nd light source 241,242 Wedge prism 25 Prism 26 Cylinder lens 27 Polygon lens LB1, LB2 Laser beam 3 Position detector (CCD)

Claims (6)

Laser beams emitted from a plurality of light sources are irradiated to a polygon mirror so that adjacent laser beams form a predetermined angle Δθ with each other in the main scanning direction, and the reflected light of each laser beam from the polygon mirror is irradiated to a photosensitive drum. A method of manufacturing a multi-beam type laser beam scanning unit,
Based on the predetermined angle Δθ, the position of the reflected light of each laser beam irradiated on the photosensitive drum in the sub-scanning direction, and the beam pitch in the sub-scanning direction when forming an image on the photosensitive drum are equally spaced. position adjustment step of adjusting in order to possess,
In the position adjustment step, the beam pitch P (mm) in the sub-scanning direction on the photosensitive drum is
P = 25.4 / D × (1−Δθ × M × N / (4 × π))
here,
D: Resolution in the sub-scanning direction (dpi)
Δθ: angle (rad) formed by adjacent laser beams
M: Number of polygon mirror faces
N: Number of light sources
The method of manufacturing a laser beam scanning unit according to claim 1, wherein the position of the reflected light in the sub-scanning direction is adjusted to satisfy the above condition . In the position adjusting step, by rotating the disposed a wedge prism between the polygon mirror and the plurality of light sources, according to claim 1, characterized in that to adjust the sub-scanning direction of the position of the reflected light A manufacturing method of the laser beam scanning unit described in 1. The position adjustment step includes
A detection preparation step of disposing a position detector on the image plane for detecting the position of the reflected light in the main scanning direction and the sub-scanning direction;
A first detection step of fixing the polygon mirror at a predetermined position, causing one of the plurality of light sources to emit light, and detecting positions in the main scanning direction and the sub-scanning direction by the position detector; ,
A second detection step of emitting a light source adjacent to the one light source among the plurality of light sources and detecting a position in a main scanning direction by the position detector;
The polygon to match the position in the main scanning direction corresponding to the other light source obtained in the second detection step with the position in the main scanning direction corresponding to the first light source obtained in the first detection step. A mirror rotation process for rotating the mirror;
A third detection step of causing the other light source to emit light after the mirror rotation step and detecting a position in the sub-scanning direction by the position detector;
The interval between the position in the sub-scanning direction corresponding to the other light source obtained in the third detection step and the position in the sub-scanning direction corresponding to the first light source obtained in the first detection step is 3. The method of manufacturing a laser beam scanning unit according to claim 2 , further comprising an adjusting step of rotating the wedge prism disposed between the other light source and the polygon mirror so as to obtain a beam pitch P. . The method of manufacturing a laser beam scanning unit according to claim 3 , wherein the position detector includes a CCD (Charge Coupled Devices). Wherein the predetermined position is a position in the main scanning direction of the reflected light, a main scanning direction of the scanning range laser beam scanning unit according to claim 3 or claim 4, characterized in that substantially a center to be located in Manufacturing method. Laser beams emitted from a plurality of light sources are irradiated to a polygon mirror so that adjacent laser beams form a predetermined angle Δθ with each other in the main scanning direction, and the reflected light of each laser beam from the polygon mirror is irradiated to a photosensitive drum. A method for adjusting a multi-beam laser beam scanning unit,
Based on the predetermined angle Δθ, the position of the reflected light of each laser beam irradiated on the photosensitive drum in the sub-scanning direction, and the beam pitch in the sub-scanning direction when forming an image on the photosensitive drum are equally spaced. Adjust as much as possible,
The beam pitch P (mm) in the sub-scanning direction on the photosensitive drum is
P = 25.4 / D × (1−Δθ × M × N / (4 × π))
here,
D: Resolution in the sub-scanning direction (dpi)
Δθ: angle (rad) formed by adjacent laser beams
M: Number of polygon mirror faces
N: Number of light sources
A method of adjusting a laser beam scanning unit, wherein the position of the reflected light in the sub-scanning direction is adjusted to satisfy the above condition.