JP2017187697A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner capable of appropriately controlling a temporal deviation amount when a plurality of luminous fluxes split from a luminous flux from a light source is made to alternately scan the respective scanning target surfaces.SOLUTION: The optical scanner relating to the present invention includes: a deflector for deflecting first and second luminous fluxes to optically scan effective regions of first and second scanning target surfaces; an incident optical system for allowing the first and second luminous fluxes to be incident to the deflector; and an imaging optical system for guiding the first and second luminous fluxes deflected by the deflector to the first and second scanning target surfaces, respectively. The deflector includes N pieces of deflecting surfaces rotating around a rotation axis; and the incident optical system includes a splitting element for splitting a luminous flux from a light source into the first and second luminous fluxes. In a main scanning cross-section, angles α1, α2 formed by incident directions of the first and second luminous fluxes to the deflector and the optical axis of the imaging optical system, respectively, and a ratio D of an effective scanning angle corresponding to the effective region with respect to the whole scanning angle of the deflector satisfy conditions represented by α2≤α1-2×360/N×D and α2≥α2-2×360/N×(1-D).SELECTED DRAWING: Figure 3

Description

  The present invention relates to an optical scanning device, and is particularly suitable for an image forming apparatus such as a laser beam printer or a multifunction printer (multifunction printer).

  In recent years, an optical scanning device has been used as an exposure device for an image forming apparatus such as a laser beam printer.

Patent Document 1 discloses an optical scanning device 500 as shown in FIG.
As shown in FIG. 6, a light beam emitted from a common light source (not shown) is split into two light beams L1 and L2 by a light beam splitting means (not shown). Then, the light beam L2 is reflected by the folding mirrors M51 and M52, and the light beams L1 and L2 enter the deflecting / reflecting surface 551 of the polygon mirror 505 so that the difference in incident angle in the main scanning section is 45 °.
At this time, the two light beams L1 and L2 perform optical scanning alternately on each of the two corresponding scanned surfaces while shifting the time.

JP 2005-92129 A

However, in the optical scanning device disclosed in Patent Document 1, the timing for alternately scanning a plurality of scanned surfaces is not accurately set. Further, depending on the angle at which the light beam enters the deflecting reflection surface of the deflector, there is a problem that return light is generated.
That is, the time for scanning the surface to be scanned is not taken into consideration, and the time when the plurality of light beams obtained by dividing the light beam emitted from the common light source alternately scan the surface to be scanned is scanned. The amount of misalignment is not controlled. Therefore, synchronization detection and APC control that should be performed at a timing when the surface to be scanned is not printed cannot be performed appropriately.

  Therefore, the present invention can appropriately control the amount of time deviation when a plurality of light beams obtained by splitting light beams emitted from a common light source alternately scan the surface to be scanned. An object of the present invention is to provide an optical scanning device that can be used.

The optical scanning device according to the present invention deflects the first light beam and the second light beam, and optically scans the effective area of the first scanned surface and the effective area of the second scanned surface in the main scanning direction. A deflector, an incident optical system for causing the first and second light beams to enter the deflector, and the first and second light beams deflected by the deflector are guided to the first and second scanned surfaces, respectively. An imaging optical system, and the deflector includes N deflecting surfaces that rotate about a rotation axis parallel to the sub-scanning direction, and the incident optical system receives the first and first light beams emitted from the light source. A splitting element that splits the light beam into two light beams, and in the main scanning section, the angles formed by the incident directions of the first and second light beams into the deflector and the optical axis of the imaging optical system are α1 and When the ratio of α2 and the effective scanning angle corresponding to the effective region to the total scanning angle of the deflector is D,
α2 ≦ α1-2 × 360 / N × D
α2 ≧ α1-2 × 360 / N × (1-D)
It satisfies the following condition.

  According to the present invention, it is possible to appropriately control the amount of time shift when a plurality of light beams obtained by dividing a light beam emitted from a common light source alternately scans the surface to be scanned. An optical scanning device that can be provided can be provided.

FIG. 3 is a partially enlarged main scanning sectional view of the optical scanning device according to the first embodiment. FIG. 3 is a partially enlarged main scanning sectional view of the optical scanning device according to the first embodiment and a diagram showing an optical path of each light beam. 1 is a main scanning sectional view of an optical scanning device according to a first embodiment, a diagram showing an optical path of each light beam, and a partially enlarged sub-scanning sectional view. The main scanning sectional view of the optical scanning device concerning a second embodiment, and the figure showing the optical path of each light beam. 1 is a cross-sectional view of main parts of a color image forming apparatus equipped with an optical scanning device according to an embodiment of the present invention. FIG. 6 is a partially enlarged main scanning sectional view of a conventional optical scanning device.

  Hereinafter, the optical scanning device according to the present embodiment will be described with reference to the drawings. It should be noted that the drawings shown below may be drawn at a scale different from the actual scale so that the present embodiment can be easily understood.

  In the following description, the main scanning direction corresponds to a direction perpendicular to the rotation axis of the deflector and the optical axis of the optical system, and the sub-scanning direction corresponds to a direction parallel to the rotation axis of the deflector. The main scanning section corresponds to a section perpendicular to the sub scanning direction, and the sub scanning section corresponds to a section perpendicular to the main scanning direction.

  FIG. 6 is a partially enlarged main scanning sectional view of the optical scanning device 500 disclosed in Patent Document 1. In FIG.

  As shown below, in Patent Document 1, since there is no discussion of the return light in the optical scanning device 500, the two light beams L1 and L2 obtained by dividing the light beam emitted from the common light source are used. While one of the light beams L1 is printing on the surface to be scanned, there is a problem that the amount of light emitted from the light beam L1 during printing becomes unstable due to the reflected light beam L21 of the other light beam L2.

  As shown in FIG. 6, a light beam emitted from a common light source (not shown) is split into light beams L1 and L2 by a light beam splitting unit (not shown). Thereafter, the light beam L1 travels straight and enters the deflection surface (deflection reflection surface) 551 of the polygon mirror 505, while the light beam L2 is reflected by the folding mirrors M51 and M52 and enters the deflection reflection surface 551.

  Here, when the optical axis 560 of the imaging lens 506 is the X axis, the angles formed by the incident directions of the light beams L1 and L2 on the deflecting reflection surface 551 and the X axis in the main scanning section are α1 and α2, respectively. Then, α1 = 90 ° and α2 = 45 °.

At the timing shown in FIG. 6, the angle θ formed by the normal line 552 of the deflecting / reflecting surface 551 with respect to the X axis in the main scanning section is 45 °.
At this time, the light beam L1 incident on the deflecting / reflecting surface 551 is deflected and reflected, and the deflected and reflected light beam L11 travels parallel to the optical axis 560, and is formed on an axial image on a scanning surface (not shown) by the imaging lens 506. High image is formed and printed.
On the other hand, since the light beam L2 is perpendicularly incident on the deflecting / reflecting surface 551, the light beam L21 which has been deflected and reflected becomes a so-called return light that returns to the light source by reversing the optical path of the light beam L2.

  Such return light, after reaching the light emitting point of the light source, enters an APC sensor (not shown) that monitors the light emission amount of the light source. Since a light source such as a semiconductor laser controls the light emission amount of the light source so as to obtain a desired light amount based on the light amount detected by the APC sensor, the APC sensor emits light when the return light is incident. The amount cannot be measured correctly, and the light emission amount becomes unstable.

  Further, at the timing shown in FIG. 6, when the light beam L11 deflected and reflected by the deflecting / reflecting surface 551 prints on the surface to be scanned (not shown), the light beam L21 deflected and reflected by the deflecting / reflecting surface 551 returns. Of course, there is also a timing when the light beam L11 becomes return light when the light beam L21 is printed.

  As will be described below, in the optical scanning device according to the present embodiment, the light emission amount of the light source can be stabilized without generating such return light.

[First embodiment]
First, each conditional expression satisfied by the optical scanning device 100 according to the first embodiment will be described.
FIGS. 1A and 1B are partial enlarged main scanning cross-sectional views of an example of the optical scanning device 100 according to the first embodiment. FIG. 1C shows a partially enlarged main scanning sectional view of a modification of the optical scanning device 100 according to the first embodiment.
In FIG. 1B, the half mirror M1, the folding mirror M2, and the imaging lens 6 are not shown for simplification of the drawing.

In the cases shown in FIGS. 1A and 1B, a light beam L emitted from a light source (not shown) is transmitted by a half mirror M1 as a splitting element and transmitted light beam (first light beam) L1 and reflected light beam ( The second luminous flux L2 is divided.
The light beam L1 transmitted through the half mirror M1 is incident on the deflection reflection surface 51 of the polygon mirror (deflector) 5. On the other hand, the light beam L <b> 2 reflected by the half mirror M <b> 1 is reflected by the folding mirror M <b> 2 and enters the deflecting / reflecting surface 51 of the polygon mirror 5.

In the case shown in FIG. 1C, a light beam L emitted from a light source (not shown) is split into a transmitted light beam L1 and a reflected light beam L2 by a half mirror M1 as a splitting element.
The light beam L1 transmitted through the half mirror M1 is incident on the deflection reflection surface 54 of the polygon mirror (deflector) 5. On the other hand, the light beam L <b> 2 reflected by the half mirror M <b> 1 is reflected by the folding mirror M <b> 2 and enters the deflecting / reflecting surface 51 of the polygon mirror 5.

  That is, as the polygon mirror 5 rotates, the deflecting / reflecting surface 51 deflects and scans the light beam L2 after deflecting and scanning the light beam L1. Then, the deflecting / reflecting surface 54 adjacent to the deflecting / reflecting surface 51 deflects and scans the light beam L1, and then deflects and scans the light beam L2.

  Here, when the optical axis 60 of the imaging lens is the X axis, the angle formed by the X axis and the incident direction of the light beam L1 on the deflecting / reflecting surface in the main scanning section (hereinafter sometimes referred to as main scanning incident angle). A) is α1. In addition, an angle formed by the incident direction of the light beam L2 on the deflecting reflecting surface and the X axis in the main scanning section is α2.

  The angles α1 and α2 are set such that the light beams L1 and L2 alternately perform optical scanning while shifting different scanning surfaces in time.

Hereinafter, in order to simplify the explanation, it is assumed that α1> α2 and α1> 0.
As for the angles α1 and α2, the angle formed counterclockwise from the X axis around the axis parallel to the rotation axis 50 of the polygon mirror 5 is positive.
That is, the example shown in FIGS. 1A and 1B shows a case where α2> 0 and α1-α2 are relatively small. In the example shown in FIG. This shows a case where α2 <0 and α1-α2 are relatively large.
The polygon mirror 5 is rotated in the direction of the arrow 53.
Note that the present embodiment is not limited to this condition.

As shown in FIGS. 1A to 1C, the normal line of the deflecting and reflecting surface 51 of the polygon mirror 5 is H1, and the angle between the normal line H1 and the X axis in the main scanning section is θ. To do.
Further, the polygon mirror 5 has four deflecting and reflecting surfaces, that is, the number N of surfaces of the polygon mirror 5 is four.

The light beams L1 and L2 deflected by the polygon mirror 5 scan different scanning surfaces (not shown) by the imaging lens 6, respectively.
Here, as shown in FIGS. 1A to 1C, the traveling direction immediately after the light beam traveling toward the most off-axis image height Y + on the scanning start side on the scanned surface is reflected by the deflecting reflecting surface. The angle formed by G + and the X axis is the most off-axis scanning angle + ωmax. Further, the angle formed between the traveling direction G- and the X axis immediately after being reflected by the deflecting / reflecting surface of the light beam toward the most off-axis image height Y- on the scanning end side on the scanned surface is the most off-axis scanning angle -ωmax. And

The polygon mirror having N rotating surfaces is scanned by one deflecting reflection surface by the reflected light beam (angle formed by the light beam deflected and reflected by the deflecting reflection surface in the main scanning section and the X axis) 2 ×. Deflection scanning can be performed by 360 / N (degrees). Here, the scanning angle range of 2 × 360 / N (degrees), that is, the scanning angle range in the main scanning section that can be scanned by one deflecting reflection surface is referred to as a full scanning angle.
On the other hand, in the effective area (printing area) of the scanned surface, the range of the scanning angle of the light beam that scans the entire image height from the most off-axis image height Y + to the most off-axis image height Y− This corresponds to 2 × ωmax.

Therefore, the ratio D of the print scan angle to the total scan angle is
D = 2 × ωmax / (2 × 360 / N)
From this, the most off-axis angle ωmax is
ωmax = 360 / N × D
It can be expressed as.

In the optical scanning device 100 according to the present embodiment, since the light beams L1 and L2 are deflected and scanned, D is the ratio of the total scanning angle to the printing scanning angle with respect to the light beam L1, or the total scanning angle and printing with respect to the light beam L2. In other words, the ratio to the scanning angle.
Further, since the polygon mirror 5 rotates at a constant speed, the light beams L1 and L2 are sequentially deflected by the same deflecting / reflecting surface, so that the scanned surfaces where the light beams L1 and L2 are different from each other temporally. The optical scanning is started alternately.
Therefore, the optical scanning device 100 according to the present embodiment is configured such that the ratio of the time for printing an image within a predetermined time is D + D = 2 × D.

  Next, the setting of the main scanning incident angle α1 of the light beam L1 and the main scanning incident angle α2 of the light beam L2 will be described in detail.

  First, in the optical scanning device 100 according to the present embodiment, conditions for avoiding overlapping of printing times of the light beam L1 and the light beam L2 will be described.

If the angles α1 and α2 are sufficiently close, the printing time by the light beam L1 and the printing time by the light beam L2 overlap, that is, the light beams L1 and L2 are temporarily printed simultaneously. End up.
Therefore, it is necessary to set the angles α1 and α2 so that the printing time by the light beam L1 and the printing time by the light beam L2 are appropriately separated.

  As described above, in the optical scanning device 100 according to the present embodiment, as the polygon mirror 5 rotates, the deflecting / reflecting surface 51 deflects and scans the light beam L2 after deflecting and scanning the light beam L1. Then, the deflecting / reflecting surface 54 adjacent to the deflecting / reflecting surface 51 deflects and scans the light beam L1, and then deflects and scans the light beam L2.

At this time, it is necessary to consider two conditions.
The first condition is that the printing time when the deflecting / reflecting surface 51 deflects and scans the light beam L1 and the printing time when the deflecting / reflecting surface 51 deflects and scans the light beam L2 do not overlap.
The second condition is that the printing time when the deflecting / reflecting surface 51 deflects and scans the light beam L2 does not overlap with the printing time when the deflecting / reflecting surface 54 scans and deflects the light beam L1.
The two conditions must be satisfied at the same time, but this first condition needs to be considered especially when α1-α2 is small, while the second condition needs to be considered especially when α1-α2 is large. is there.

First, the first condition is examined.
Regarding the first condition, the light beam L1 is deflected and reflected in the G-direction and printed at the most off-axis scanning angle -ωmax. The light beam L2 is deflected and reflected in the G + direction and the most off-axis scanning angle + ωmax. This can be achieved before the printing timing.
Specifically, the difference between the deflection angle of the light beam L1 by the deflection reflection surface 51 and the deflection angle of the light beam L2 by the deflection reflection surface 51 is the deflection angle from the most off-axis image height Y + to the most off-axis image height Y−. The angles α1 and α2 may be set so as to be 2 × ωmax or more.

Since the main scanning incident angle of the light beam L1 and the normal angle of the deflection reflection surface 51 are α1 and θ, respectively, the deflection angle of the light beam L1 by the deflection reflection surface 51 is 2 × θ−α1.
Further, since the main scanning incident angle of the light beam L2 and the normal angle of the deflection reflection surface 51 are α2 and θ, respectively, the deflection angle of the light beam L2 by the deflection reflection surface 51 is 2 × θ−α2.
Accordingly, the difference between the deflection angle of the light beam L1 by the deflection reflection surface 51 and the deflection angle of the light beam L2 by the deflection reflection surface 51 only needs to be 2 × ωmax or more, and the following conditional expression (1) should be satisfied.
(2 × θ−α2) − (2 × θ−α1) ≧ 2 × ωmax (1)
Here, an expression of α1−α2 ≧ 2 × ωmax is obtained from the conditional expression (1), and the following conditional expression (2) is obtained by substituting ωmax = 360 / N × D into this.
α1-α2 ≧ 2 × 360 / N × D (2)

Next, the second condition will be examined.
Regarding the second condition, the timing at which the light beam L2 is deflected and reflected in the G− direction and printed at the most off-axis scanning angle −ωmax is the timing at which the light beam L1 is deflected and reflected in the G + direction and the most off-axis scanning angle + ωmax. This can be achieved before the printing timing.
Specifically, the difference between the deflection angle of the light beam L2 by the deflection reflection surface 51 and the deflection angle of the light beam L1 by the deflection reflection surface 54 is a deflection angle from the most off-axis image height Y + to the most off-axis image height Y−. The angles α1 and α2 may be set so as to be 2 × ωmax or more.

Since the main scanning incident angle of the light beam L2 and the normal angle of the deflection reflection surface 51 are α2 and θ, respectively, the deflection angle of the light beam L2 by the deflection reflection surface 51 is 2 × θ−α2.
Further, since the main scanning incident angle of the light beam L1 and the angle of the normal line H2 of the deflection reflection surface 54 are α1 and θ ′ = (θ + 360 / N), respectively, the deflection angle of the light beam L1 by the deflection reflection surface 54 is 2 ×. (Θ + 360 / N) −α1.
Therefore, the difference between the deflection angle of the light beam L2 by the deflection reflection surface 51 and the deflection angle of the light beam L1 by the deflection reflection surface 54 only needs to be 2 × ωmax or more, and the following conditional expression (3) may be satisfied.
(2 × (θ + 360 / N) −α1) − (2 × θ−α2) ≧ 2 × ωmax (3)
Here, from the conditional expression (3), an expression of α2 ≧ α1 + 2 × (ωmax−360 / N) is obtained, and substituting ωmax = 360 / N × D into the following conditional expression (4) is obtained. .
α2 ≧ α1-2 × 360 / N × (1-D) (4)

  Next, in the optical scanning device 100 according to the present embodiment, third to ninth conditions for preventing one of the light beam L1 and the light beam L2 from returning to the light source during printing and the other from returning to the light source will be described. To do.

  Here, as shown in FIG. 1B, when the normal line of the deflecting / reflecting surface 51 of the polygon mirror 5 is directed in the H3 direction, the light beam L1 incident on the deflecting / reflecting surface 51 is converted into the surface to be scanned. It is assumed that the reflected light is deflected and reflected in the G + direction toward the most off-axis image height Y + on the scanning start side. Further, when the normal line of the deflecting / reflecting surface 51 of the polygon mirror 5 is directed in the H4 direction, the light beam L1 incident on the deflecting / reflecting surface 51 is at the most off-axis image height Y− on the scanning end side on the scanned surface. It is assumed that the reflected light is deflected and reflected in the G-direction.

First, the third condition is a condition in which the light beam L2 returns to the light source along the optical path of the light beam L2 and does not become return light while the light beam L1 is deflected and reflected by the deflecting / reflecting surface 51 and printed. is there.
This condition is that the incident direction of the light beam L2 is deflected and reflected when the light beam L1 is deflected and reflected by the deflecting and reflecting surface 51, that is, while the normal line of the deflecting and reflecting surface 51 changes from the H3 direction to the H4 direction. This can be achieved by setting the angles α1 and α2 so as not to coincide with the normal direction of the surface 51.

As described above, since the deflection angle of view of the light beam L1 by the deflecting reflection surface 51 is 2 × θ−α1, the following expression (5) is satisfied.
−ωmax ≦ 2 × θ−α2 ≦ + ωmax (5)
Here, when the formula (5) is modified, the following formula (6) is obtained.
(Α1-ωmax) / 2 ≦ θ ≦ (α1 + ωmax) / 2 (6)

Here, since the third condition is to set α2 so as not to be θ, the following conditional expression (7a) or (7b) may be satisfied.
α2 <(α1-ωmax) / 2 (7a)
α2> (α1 + ωmax) / 2 (7b)
If ωmax = 360 / N × D is substituted into conditional expressions (7a) and (7b), the following conditional expression (8a) or (8b) may be satisfied as the third condition.
α2 <(α1-360 / N × D) / 2 (8a)
α2> (α1 + 360 / N × D) / 2 (8b)

Next, the fourth condition is that the light beam L1 is returned to the light source along the optical path of the light beam L1 by the deflecting / reflecting surface 51 while the light beam L2 is deflected and reflected by the deflecting / reflecting surface 51 and printed. It is.
This condition is that the incident direction of the light beam L1 is deflected and reflected when the light beam L2 is deflected and reflected by the deflecting and reflecting surface 51, that is, while the normal line of the deflecting and reflecting surface 51 changes from the H3 direction to the H4 direction. This can be achieved by setting the angles α1 and α2 so as not to coincide with the normal direction of the surface 51.

As described above, since the deflection angle of the light beam L2 by the deflecting reflection surface 51 is 2 × θ−α2, the following equation (9) is satisfied.
−ωmax ≦ 2 × θ−α2 ≦ + ωmax (9)
Here, when the formula (9) is modified, the following formula (10) is obtained.
(Α2−ωmax) / 2 ≦ θ ≦ (α2 + ωmax) / 2 (10)

Here, since the fourth condition is to set α1 not to be θ, the following conditional expression (11a) or (11b) may be satisfied.
α1 <(α2-ωmax) / 2 (11a)
α1> (α2 + ωmax) / 2 (11b)
If ωmax = 360 / N × D is substituted into conditional expressions (11a) and (11b), the following conditional expression (12a) or (12b) may be satisfied as the fourth condition.
α2> 2 × α1 + 360 / N × D (12a)
α2 <2 × α1−360 / N × D (12b)

Next, the fifth condition is that the light beam L1 is deflected and reflected by the deflecting / reflecting surface 51 and printed, and the light beam L1 is deflected by the deflecting / reflecting surface 54 adjacent to the deflecting / reflecting surface 51 to the light source along the optical path of the light beam L1. This is a condition that the light does not return.
This condition is that the incident direction of the light beam L1 is deflected and reflected when the light beam L2 is deflected and reflected by the deflecting and reflecting surface 51, that is, while the normal line of the deflecting and reflecting surface 51 changes from the H3 direction to the H4 direction. This can be achieved by setting the angles α1 and α2 so as not to coincide with the normal direction of the surface 54.
As described above, if the angle formed by the normal line of the deflection reflection surface 51 and the X axis in the main scanning section is θ, the angle formed by the normal line of the deflection reflection surface 54 and the X axis in the main scanning section. θ ′ is θ + 360 / N.

As described above, since the deflection angle of the light beam L2 by the deflecting / reflecting surface 51 is 2 × θ−α2, the following equation (13) is satisfied.
−ωmax ≦ 2 × θ−α2 ≦ + ωmax (13)
Here, when Expression (13) is modified using θ ′ = (θ + 360 / N), the following Expression (14) is obtained.
(Α2−ωmax) / 2 + 360 / N ≦ θ ′ ≦ (α2 + ωmax) / 2 + 360 / N (14)

Here, since the fifth condition is to set α1 not to be θ ′, the following conditional expression (15a) or (15b) may be satisfied.
α1 <(α2−ωmax) / 2 + 360 / N (15a)
α1> (α2 + ωmax) / 2 + 360 / N (15b)
Further, if ωmax = 360 / N × D is substituted into the conditional expressions (15a) and (15b), the following conditional expression (16a) or (16b) may be satisfied as the fifth condition.
α2> 2 × α1−360 / N × (2-D) (16a)
α2 <2 × α1−360 / N × (2 + D) (16b)

Next, the sixth condition is a condition in which the light beam L1 returns to the light source along the optical path of the light beam L1 by the same deflecting reflection surface while the light beam L1 is deflected and reflected by the deflecting reflection surface and does not become return light. It is.
This condition is achieved by causing the light beam L1 to enter the deflecting / reflecting surface at an angle larger than the most off-axis scanning angle + ωmax corresponding to the G + direction toward the most off-axis image height Y + on the scanning surface on the scanned surface. can do.
That is, this condition corresponds to α1> ωmax, and if ωmax = 360 / N × D is substituted for this, the following condition expression (17) may be satisfied as the sixth condition.
α1> 360 / N × D (17)

Next, the seventh condition is that the light beam L2 is returned to the light source along the optical path of the light beam L2 by the same deflecting reflection surface while the light beam L2 is deflected and reflected by the deflecting reflection surface, and does not become return light. It is.
This condition is that the light beam L2 is incident on the deflecting / reflecting surface at an angle larger than the most off-axis scan angle + ωmax corresponding to the G + direction toward the most off-axis image height Y + on the scan start side, or on the scan surface. This can be achieved by making the light incident on the deflecting / reflecting surface at an angle smaller than the most off-axis scanning angle −ωmax corresponding to the G-direction toward the most off-axis image height Y− on the scanning end side on the surface.
That is, as the seventh condition, the following conditional expression (18a) or (18b) may be satisfied.
α2> ωmax (18a)
α2 <−ωmax (18a)
If ωmax = 360 / N × D is substituted into conditional expressions (18a) and (18b), the following conditional expression (19a) or (19b) may be satisfied as the seventh condition.
α2> 360 / N × D (19a)
α2 <−360 / N × D (19b)

Next, the eighth condition is that the light beam L2 is returned to the light source along the optical path of the light beam L1 by the same deflecting reflection surface while the light beam L1 is deflected and reflected by the deflecting reflection surface, and does not become return light. It is.
This condition is that the light beam L2 is incident on the deflecting / reflecting surface at an angle larger than the most off-axis scanning angle + ωmax corresponding to the G + direction toward the most off-axis image height Y + on the scanning surface on the scanning surface, or scanned This can be achieved by making the light incident on the deflecting / reflecting surface at an angle smaller than the most off-axis scanning angle −ωmax corresponding to the G-direction toward the most off-axis image height Y− on the scanning end side on the surface.
That is, it is sufficient that the conditional expression (19a) or (19b) is satisfied.

Next, the ninth condition is a condition in which the light beam L1 returns to the light source along the optical path of the light beam L2 by the same deflection reflection surface while the light beam L2 is deflected and reflected by the deflection reflection surface and does not become return light. It is.
This condition is achieved by causing the light beam L1 to enter the deflecting / reflecting surface at an angle larger than the most off-axis scanning angle + ωmax corresponding to the G + direction toward the most off-axis image height Y + on the scanning surface on the scanned surface. can do.
That is, it is only necessary that the conditional expression (17) is satisfied.

As described above, the optical scanning device 100 according to the present embodiment satisfies the first to ninth conditions, so that the light beam L emitted from a single light source is converted into the light beam L1 and the light beam L2 by the half mirror M1. It is possible to divide each of them and enter the deflector 5 at different angles α1 and α2, and perform deflection scanning by shifting the timing for printing different surfaces to be scanned.
Then, the scanning surface is printed by controlling the amount of time deviation when the plurality of light beams obtained by dividing the light beams emitted from the common light source alternately scan each scanning surface. Synchronization detection and APC control to be performed at a timing that is not performed can be appropriately performed.
In addition, a plurality of light beams obtained by dividing the light beam emitted from the common light source do not return to the light source, and the light emission amount of the light source can be stabilized.
Therefore, in the optical scanning device 100 according to the present embodiment, the light emission timing and the light emission amount of the light source can be appropriately controlled when optically scanning a plurality of scanned surfaces using a light beam emitted from a single light source. it can.

  FIG. 2A is a partially enlarged main scanning sectional view of an example of the optical scanning device 100 according to the first embodiment. FIGS. 2B and 2C are diagrams showing optical paths of light beams in the optical scanning device 100 according to the first embodiment.

As shown in FIGS. 2A to 2C, a light beam L emitted from a light source (not shown) is divided into a transmitted light beam L1 and a reflected light beam L2 by a half mirror M1 as a splitting element.
The light beam L1 transmitted through the half mirror M1 is incident on the deflecting / reflecting surface 51 of the polygon mirror 5. On the other hand, the light beam L <b> 2 reflected by the half mirror M <b> 1 is reflected by the folding mirror M <b> 2 and enters the deflecting / reflecting surface 51 of the polygon mirror 5.
Here, when the optical axis 60 of the imaging lens is the X axis, the angles α1 and α2 formed by the incident directions of the light beams L1 and L2 on the deflecting reflecting surface and the X axis in the main scanning section are 90 ( Degrees) and 45 (degrees).
Also, when the axis perpendicular to the optical axis 60 in the main scanning section is the Y axis, the angle formed by the incident directions of the light beams L1 and L2 on the deflecting and reflecting surfaces and the XY plane (hereinafter referred to as the sub-scanning oblique incident angle). .Beta.1 and .beta.2 respectively.

FIG. 2A shows a case where the angle θ formed by the normal line H1 of the deflection reflection surface 51 of the polygon mirror 5 and the X axis in the main scanning section is 45 (degrees).
At this time, the light beam L1 is deflected and reflected by the deflection reflection surface 51 in a direction parallel to the optical axis 60 in the main scanning section. On the other hand, the main scanning incident angle α1 of the light beam L2 coincides with the normal angle θ of the deflecting / reflecting surface 51, that is, the light beam L2 faces the deflecting / reflecting surface 51.
Thereby, the reflected light beam L21 of the light beam L2 by the deflecting reflection surface 51 returns to the light source along the incident optical path of the light beam L2.

FIG. 2C shows the optical paths of the light beams L2 and L21. As shown in FIG. 2C, the light beams L2 and L21 include a marginal ray in addition to the principal ray.
Here, if the sub-scanning oblique incidence angle β2 of the light beam L2 is sufficiently large, the optical path of the light beam L21 is sufficiently separated from the optical path of the light beam L2. On the other hand, when the sub-scanning oblique incident angle β2 of the light beam L2 is small, the optical path of the light beam L21 overlaps the optical path of the light beam L2, and a part of the light beam L21 passes along the optical path of the light beam L2 to the light source. Back, it becomes a return light.

Accordingly, when the spread angle of the marginal ray in the sub-scan section of the light beam L2 is NA2, if β2 is set so as to satisfy | β2 |> NA2, the light beam L21 does not become return light.
Actually, since the angles β2 and NA2 vary due to tolerance, it is desirable that the optical scanning device 100 according to the present embodiment satisfies the following conditional expression (20) in consideration of the variation.
| Β2 |> K × NA2 (20)
Here, K is a coefficient indicating the degree of variation due to the tolerance of the angles β2 and NA2.
In particular, experience has shown that K ≦ 1.31 even when the deterioration of wavefront aberration is taken into account as a tolerance.

Similarly, for the light beam L1, when β1 is set so as to satisfy | β1 |> NA1, where NA1 is the spread angle of the marginal ray of the light beam L1 in the sub-scan section, the light beam L1 by the deflecting reflecting surface 51 The reflected light beam L11 is not returned light.
Further, the following conditional expression (21)
| Β1 |> K × NA1 (21)
More preferably, β1 is set so as to satisfy the above condition.

3A and 3B are main scanning sectional views of the optical scanning device 100 according to the present embodiment. FIG. 3C is a diagram showing the optical path of each light beam in the optical scanning device 100 according to the present embodiment. FIG. 3D is a partially enlarged sub-scan sectional view of the optical scanning device 100 according to the present embodiment.
In FIG. 3A, the folding mirror M3 and the cylinder lens 42 are not shown, and only the optical path of the light beam L1 transmitted through the half mirror M1 is shown. On the other hand, in FIG. 3B, the folding mirror M2 and the cylinder lens 41 are not shown, and only the optical path of the light beam L2 reflected by the half mirror M1 is shown.

  The optical scanning device 100 includes a light source 1, a diaphragm 2, a condenser lens 3, cylinder lenses 41 and 42, a half mirror M1 as a splitting element, and folding mirrors M2 and M3. The optical scanning device 100 includes a polygon mirror 5 as a deflector, a first imaging lens 61, second imaging lenses 62 and 63, and folding mirrors M4, M5, and M6.

As the light source 1, a semiconductor laser having a light emitting point is used. There may be a plurality of light emitting points. The light source 1 is provided with a cover glass (not shown).
The diaphragm 2 has a rectangular opening, and restricts the diameter of the light beam L emitted from the light source 1 in the main scanning direction and the sub-scanning direction. The size of the rectangular opening of the diaphragm 2 according to the present embodiment is 5.60 mm in the main scanning direction × 0.76 mm in the sub-scanning direction. Further, instead of the diaphragm 2, a main scanning diaphragm for limiting the light beam diameter of the light beam in the main scanning direction and a sub-scanning diaphragm for limiting the light beam diameter of the light beam in the sub-scanning direction may be provided separately.
The condenser lens 3 converts the light beam L that has passed through the diaphragm 2 into a substantially parallel light beam in both the main scanning direction and the sub-scanning direction. Here, the substantially parallel light beam includes a weak divergent light beam, a weakly convergent light beam, and a parallel light beam.
The half mirror M1 splits the light beam L that has passed through the condenser lens 3 into a transmitted light beam (first light beam) L1 and a reflected light beam (second light beam) L2.
The folding mirrors M2 and M3 reflect the transmitted light beam L1 and the reflected light beam L2 divided by the half mirror M1, respectively.
Each of the cylinder lenses 41 and 42 has a predetermined refractive power only in the sub-scanning direction, and condenses the transmitted light beam L1 and the reflected light beam L2 reflected by the folding mirrors M2 and M3, respectively, in the sub-scanning direction.

In this way, the divided light beams L1 and L2 emitted from the light source 1 are collected only in the sub-scanning direction in the vicinity of the deflecting reflection surface of the deflector 5, and formed as a long line image in the main scanning direction. Is done.
The diaphragm 2, the condensing lens 3, the cylinder lenses 41 and 42, the half mirror M1, and the folding mirrors M2 and M3 constitute an incident optical system of the optical scanning device 100 according to the present embodiment.

The polygon mirror 5 is deflected and reflected by the light beams L1 and L2 toward the scanned surfaces 71 and 72, respectively, by being rotated by driving means such as a motor (not shown).
The first imaging lens 61 is configured to image the light beams L1 and L2 deflected and reflected by the polygon mirror 5 on the scanned surfaces 71 and 72, respectively.
The folding mirrors M4 and M5 reflect the light beam L1 that has passed through the first imaging lens 61.
The second imaging lens 62 images the light beam L1 reflected by the folding mirrors M4 and M5 on the surface to be scanned (first surface to be scanned) 71.
The folding mirror M6 reflects the light beam L2 that has passed through the first imaging lens 61.
The second imaging lens 63 forms an image of the light beam L2 reflected by the folding mirror M6 on the surface to be scanned (second surface to be scanned) 72.
The first imaging lens 61, the second imaging lenses 62 and 63, and the folding mirrors M4, M5, and M6 constitute an imaging optical system of the optical scanning device 100 according to the present embodiment.

The light beam L emitted from the light source 1 is limited so that the diameter of the light beam in the main scanning direction and the sub-scanning direction is limited by the diaphragm 2, and is converted by the condenser lens 3 so as to be a substantially parallel light beam in both the main scanning direction and the sub-scanning direction. The light beam L1 is divided into a transmitted light beam L1 and a reflected light beam L2 by the half mirror M1.
The transmitted light beam L1 and the reflected light beam L2 are reflected by the folding mirrors M2 and M3, condensed by the cylinder lenses 41 and 42 in the sub-scanning direction, and enter the deflecting / reflecting surface of the deflector 5.
The light beams L1 and L2 incident on the deflecting / reflecting surface of the deflector 5 are deflected and reflected by the deflecting / reflecting surface of the deflector 5, and then the first imaging lens 61, the second imaging lenses 62 and 63, and Images are formed on the scanned surfaces 71 and 72 by the folding mirrors M4, M5, and M6.
In this way, a spot-like image is formed in the vicinity of the scanned surfaces 71 and 72 in both the main scanning section and the sub-scanning section, and by rotating the deflector 5 at a constant speed, The scanning surfaces 71 and 72 can be scanned at a constant speed.

  Note that the first imaging lens 61 and the second imaging lenses 62 and 63 of the optical scanning device 100 according to the present embodiment are made of resin. Since a resin lens is manufactured by a known molding technique in which a resin is filled in a mold and taken out from the mold after cooling, it can be manufactured at a lower cost than a conventional imaging lens using a glass lens.

As shown in FIG. 3C, in the optical scanning device 100 according to this embodiment, the light beams L1 and L2 are deflected at an angle β from the lower side and the upper side in the sub-scanning direction, respectively. A so-called sub-scanning oblique incidence optical system that is incident on the deflecting reflecting surface of the device 5 is employed. Hereinafter, this angle β may be referred to as a sub-scanning oblique incident angle.
As a result, as shown in FIG. 3D, the light beams L1 and L2 that have passed through the first imaging lens 61 can be optically separated by the folding mirror M4.

  Next, various characteristics of the optical scanning device 100 according to the present embodiment are shown in Tables 1 to 6 below.

In Tables 3 and 5, “E-x” means “× 10 ^−x ”.
In the following, the optical axis direction of the first imaging lens 61, the axis orthogonal to the optical axis in the main scanning section, and the axis orthogonal to the optical axis in the sub-scanning section are the X axis and Y axis, respectively. And the Z axis.
In Table 2, R is the radius of curvature of each surface, X, Y, and Z are the coordinates of the surface vertex position of each surface, and gx (x), gx (y), and gx (z) are The normal vector component at the surface vertex position is shown.

As shown in Table 1, in the optical scanning device 100 according to the present embodiment, the angles α1 and α2 formed by the incident directions of the light beams L1 and L2 on the deflecting reflection surfaces and the X axis in the main scanning section are as follows. They are 50 (degrees) and -50 (degrees), respectively.
Further, as shown in Table 1, in the optical scanning device 100 according to the present embodiment, the angles β1 and β2 formed by the incident directions of the light beams L1 and L2 on the deflection reflection surface and the XY plane are 1 respectively. .8 (degrees) and -1.8 (degrees).
In the optical scanning device 100 according to the present embodiment, the angle β0 formed by the incident direction of the light beam L emitted from the light source 1 and the XY plane with respect to the half mirror M1 is 4.8 (degrees).
The half mirror M1 and the folding mirrors M2 and M3 are appropriately arranged so as to have such an angle.

The generatrix shape (lens surface shape in the main scanning section) of the entrance surface and exit surface of each lens of the optical scanning device 100 according to the present embodiment is a function up to the 10th order as in the following equation (22). Is an aspherical shape that can be expressed as

Here, the intersection of each lens surface and the optical axis is the origin, Ry is the radius of curvature of the generatrix, Ky is the eccentricity, and b _i (i = 4, 6, 8, 10) is the aspherical coefficient.
Regarding y, the side on which the light source 1 of the optical scanning device 100 is disposed and the side on which the light source 1 is not disposed are defined as a plus side and a minus side, respectively. When the coefficient in the positive and negative sides Ry, Ky and b _i are different, as shown in Table 3 and Table 5 are denoted by the subscript u is the coefficient of plus side (i.e., Ryu, Kyu, b _iu ), subscript l is attached to the negative side coefficient (that is, Ryl, Kyl and b _il ). In this case, the bus bar shape is asymmetric in the main scanning direction.

ここで、Ｓは母線方向の各々の位置における母線の法線を含み主走査断面と垂直な面内に定義される子線形状である。 Also, the sub-line shapes (lens surface shapes in the sub-scanning section at an arbitrary image height) of the entrance surface and the exit surface of each lens of the optical scanning device 100 according to the present embodiment are expressed by the following equation (23). It is such an aspherical shape.

Here, S is a child line shape defined in a plane perpendicular to the main scanning section including the normal line of the bus line at each position in the bus line direction.

ここで、ｒは光軸上における子線曲率半径、ｄ_j（ｊ＝２、４、６、８、１０）は子線曲率半径の変化係数である。なお、ｙに関してプラス側とマイナス側で係数ｄ_jが異なる場合は、表３及び表５にあるように、プラス側の係数には添字ｕを付し（すなわち、ｄ_ju）、マイナス側の係数には添字ｌを付している（すなわち、ｄ_jl）。この場合、子線形状は、主走査方向において非対称な形状となる。 Further, the sub-curvature radius of curvature r ′ continuously changes according to the y coordinate of the lens surface as shown in the following formula (24).

Here, r is a sub-wire curvature radius on the optical axis, and d _j (j = 2, 4, 6, 8, 10) is a change coefficient of the sub-wire curvature radius. When the coefficient _dj is different between the positive side and the negative side with respect to y, as shown in Tables 3 and 5, the positive side coefficient is attached with the subscript u (that is, d _ju ), and the negative side coefficient is added. Is suffixed with l (ie, d _jl ). In this case, the child wire shape is asymmetric in the main scanning direction.

  In the present embodiment, the generatrix shape and the child wire shape of the lens surface of each lens are defined by the functions represented by Expression (22) and Expression (23), respectively. You can define it.

As shown in Tables 2 to 5, the lens surface shape of the first imaging lens 61 mainly having power in the main scanning section is an aspherical shape expressed by the above function.
The first imaging lens 61 is a convex meniscus lens having a large power in the main scanning section, a non-circular lens surface shape in the main scanning section, and a concave surface facing the deflector 5 side.
Further, the shape of the first imaging lens 61 in the main scanning section is symmetric with respect to the optical axis.
In addition, the first imaging lens 61 has a substantially non-power in which the entrance surface and the exit surface have the same curvature in the sub-scan section, but may have a cylindrical shape in which both surfaces are flat in the sub-scan direction.
The first imaging lens 61 is mainly responsible for imaging in the main scanning direction with respect to the incident light flux.

On the other hand, as shown in Tables 2 to 5, the second imaging lenses 62 and 63 are anamorphic lenses mainly having power in the sub-scan section.
The lens surface shapes of the second imaging lenses 62 and 63 are aspherical shapes expressed by the above function.
In the second imaging lenses 62 and 63, the power in the sub-scanning section is larger than the power in the main-scanning section, and the shape of the incident surface in the main-scanning section is an arc, and the shape of the other surface Is non-circular.
The shapes of the second imaging lenses 62 and 63 in the main scanning section are asymmetric with respect to the optical axis, and are substantially non-powered in the main scanning direction near the axis.
On the other hand, the shapes in the sub-scan section of the entrance and exit surfaces of the second imaging lenses 62 and 63 are convex shapes in which the curvature gradually changes from on-axis to off-axis, and are asymmetrical with respect to the optical axis. It has become.
The second imaging lenses 62 and 63 are mainly responsible for imaging in the sub-scanning direction and correcting distortion in the main scanning direction with respect to the incident light flux.
Further, as shown in Tables 2 to 5, the second imaging lenses 62 and 63 have a rotationally symmetric shape about the optical axis.

  The first imaging lens 61 and the second imaging lenses 62 and 63 have a conjugate relationship between the vicinity of the deflection reflection surface of the deflector 5 and the vicinity of the scanned surfaces 71 and 72 in the sub-scan section. Therefore, compensation for troubles is made.

  As shown in Table 6, the optical scanning device 100 according to the present embodiment has all the first to ninth conditions, that is, the conditional expressions (2), (4), (8a), (8b), ( 12a) or (12b), (16a) or (16b), (17) and (19a) or (19b) are all satisfied.

As described above, the optical scanning device 100 according to the present embodiment satisfies the first to ninth conditions, so that the light beam L emitted from a single light source is converted into the light beam L1 and the light beam L2 by the half mirror M1. It is possible to divide each of them and enter the deflector 5 at different angles α1 and α2, and perform deflection scanning by shifting the timing for printing different surfaces to be scanned.
Then, the scanning surface is printed by controlling the amount of time deviation when the plurality of light beams obtained by dividing the light beams emitted from the common light source alternately scan each scanning surface. Synchronization detection and APC control to be performed at a timing that is not performed can be appropriately performed.
Note that the synchronization detection and the APC control are desirably performed at a timing at which the return light to the light source 1 is not generated. Therefore, the normal angle θ of the deflection reflection surface 51 is θ = α1, θ = α2, or θ = (α1 + α2). This is done when it is not / 2.
Thereby, a plurality of light beams obtained by dividing the light beam emitted from the common light source do not return to the light source, and the light emission amount of the light source can be stabilized.
Therefore, in the optical scanning device 100 according to the present embodiment, the light emission timing and the light emission amount of the light source can be appropriately controlled when optically scanning a plurality of scanned surfaces using a light beam emitted from a single light source. it can.

  In the optical scanning device 100 according to the present embodiment, one light beam is emitted from the light source 1, but the present invention is not limited to this. For example, an edge emitter type monolithic laser or VCSEL that emits a plurality of light beams from a plurality of light emitting points may be used as the light source 1. The plurality of light beams emitted from the light source 1 may be divided into a plurality of transmitted light beams and a plurality of reflected light beams by the half mirror M1, and each may be guided to different scanning surfaces.

  In the optical scanning device 100 according to the present embodiment, the half mirror M1 is used as the dividing element, but the present invention is not limited to this. For example, as a splitting element, a polarizing beam splitter may be used to split a light beam into a P-polarized light beam and an S-polarized light beam, or a diffractive optical element may be used to split light beams having different diffraction orders. An effect can be obtained. The half mirror M1 is not limited to a flat plate shape, and may be a bulk shape such as a prism.

[Second Embodiment]
4A and 4B are main scanning sectional views of the optical scanning device 200 according to the second embodiment. FIG. 4C is a diagram showing the optical path of each light beam in the optical scanning device 200 according to this embodiment.
In FIG. 4A, the folding mirror M4 is not shown, and only the optical path of the light beam L1 reflected from the half mirror M1 is shown. On the other hand, in FIG. 4B, the folding mirrors M2 and M3 are not shown, and only the optical path of the light beam L2 transmitted through the half mirror M1 is shown.

The optical scanning device 200 includes a light source 1, a diaphragm 2, a condensing lens 3, a cylinder lens 4, a half mirror M1 as a splitting element, and folding mirrors M2, M3, and M4. The optical scanning device 200 includes a polygon mirror 5 as a deflector, a first imaging lens 61, second imaging lenses 62 and 63, and folding mirrors M5, M6, and M7 (not shown).
The diaphragm 2, the condensing lens 3, the cylinder lens 4, the half mirror M1, and the folding mirrors M2, M3, and M4 constitute an incident optical system of the optical scanning device 200 according to the present embodiment.
The first imaging lens 61, the second imaging lenses 62 and 63, and the folding mirrors M5, M6, and M7 constitute an imaging optical system of the optical scanning device 200 according to this embodiment.

The light beam L emitted from the light source 1 is limited so that the diameter of the light beam in the main scanning direction and the sub-scanning direction is limited by the diaphragm 2, and is converted by the condenser lens 3 so as to be a substantially parallel light beam in both the main scanning direction and the sub-scanning direction. The light is condensed in the sub-scanning direction by the cylinder lens 4.
Then, the light beam L that has passed through the cylinder lens 4 is split into a reflected light beam L1 and a transmitted light beam L2 by the half mirror M1.
Then, the reflected light beam L1 is reflected by the folding mirrors M2 and M3 and enters the deflecting reflection surface of the deflector 5. On the other hand, the transmitted light beam L2 is reflected by the folding mirror M4 and enters the deflection reflection surface of the deflector 5.
The light beams L1 and L2 incident on the deflecting / reflecting surface of the deflector 5 are reflected and deflected by the deflecting / reflecting surface of the deflector 5, respectively, and then the first imaging lens 61, the second imaging lenses 62 and 63, and Images are formed on scanned surfaces 71 and 72 by folding mirrors M5, M6, and M7.
In this way, a spot-like image is formed in the vicinity of the scanned surfaces 71 and 72 in both the main scanning section and the sub-scanning section, and by rotating the deflector 5 at a constant speed, The scanning surfaces 71 and 72 can be scanned at a constant speed.
Note that the size of the rectangular opening of the diaphragm 2 according to this embodiment is 4.80 mm in the main scanning direction × 2.20 mm in the sub-scanning direction.

  Next, various characteristics of the optical scanning device 200 according to the present embodiment are shown in Table 7 to Table 12 below.

In Tables 9 and 11, “E−x” means “× 10 ^−x ”.
In the following, the optical axis direction of the first imaging lens 61, the axis orthogonal to the optical axis in the main scanning section, and the axis orthogonal to the optical axis in the sub-scanning section are the X axis and Y axis, respectively. And the Z axis.
In Table 8, R is the radius of curvature of each surface, X, Y, and Z are the coordinates of the surface vertex position of each surface, and gx (x), gx (y), and gx (z) are The normal vector component at the surface vertex position is shown.

As shown in Table 7, in the optical scanning device 200 according to the present embodiment, the angles α1 and α2 formed by the incident directions of the light beams L1 and L2 on the deflecting reflection surfaces and the X axis in the main scanning section are as follows. They are 41 (degrees) and -41 (degrees), respectively.
Further, as shown in Table 7, in the optical scanning device 200 according to the present embodiment, the angles β1 and β2 formed by the incident directions of the light beams L1 and L2 on the deflection reflection surfaces and the XY plane are − 3.0 (degrees) and 3.0 (degrees).
In the optical scanning device 200 according to the present embodiment, the angle β0 formed by the incident direction of the light beam L emitted from the light source 1 and the XY plane with respect to the half mirror M1 is 3.0 (degrees).
The half mirror M1 and the folding mirrors M2 and M3 are appropriately arranged so as to have such an angle.

As shown in Table 7, in the optical scanning device 200 according to the present embodiment, the angles α1 and α2 formed by the incident directions of the light beams L1 and L2 on the deflecting reflection surfaces and the X axis in the main scanning section are as follows. They are 41 (degrees) and -41 (degrees), respectively.
Further, as shown in Table 7, in the optical scanning device 200 according to the present embodiment, the angles β1 and β2 formed by the incident directions of the light beams L1 and L2 on the deflection reflection surfaces and the XY plane are − 3.0 (degrees) and 3.0 (degrees).
In the optical scanning device 200 according to the present embodiment, the angle β0 formed by the incident direction of the light beam L emitted from the light source 1 and the XY plane with respect to the half mirror M1 is 3.0 (degrees).
The half mirror M1 and the folding mirrors M2 and M3 are appropriately arranged so as to have such an angle.

  As shown in Table 12, the optical scanning device 200 according to this embodiment includes all of the first to ninth conditions, that is, the conditional expressions (2), (4), (8a), (8b), ( 12a) or (12b), (16a) or (16b), (17) and (19a) or (19b) are all satisfied.

As described above, the optical scanning device 200 according to the present embodiment satisfies the first to ninth conditions, so that the light beam L emitted from a single light source is converted into the light beam L1 and the light beam L2 by the half mirror M1. It is possible to divide each of them and enter the deflector 5 at different angles α1 and α2, and perform deflection scanning by shifting the timing for printing different surfaces to be scanned.
Then, the scanning surface is printed by controlling the amount of time deviation when the plurality of light beams obtained by dividing the light beams emitted from the common light source alternately scan each scanning surface. Synchronization detection and APC control to be performed at a timing that is not performed can be appropriately performed.
Note that the synchronization detection and the APC control are desirably performed at a timing at which the return light to the light source 1 is not generated. Therefore, the normal angle θ of the deflection reflection surface 51 is θ = α1, θ = α2, or θ = (α1 + α2). This is done when it is not / 2.

Thereby, a plurality of light beams obtained by dividing the light beam emitted from the common light source do not return to the light source, and the light emission amount of the light source can be stabilized.
Therefore, in the optical scanning device 200 according to the present embodiment, the light emission timing and the light emission amount of the light source can be appropriately controlled when optically scanning a plurality of scanned surfaces using a light beam emitted from a single light source. it can.

[Various Embodiments]
Tables 13 to 18 show various characteristics and conditional expressions (2), (4), (8a), (8b), (12a), (12b), (16a), and various characteristics in the optical scanning device according to various embodiments. The calculation results of (16b), (17), (19a) and (19b) are shown.
The optical scanning device according to the various embodiments has the same configuration as the optical scanning device 100 according to the first embodiment or the optical scanning device 200 according to the second embodiment.
Tables 13 to 18 show only the number of polygon surfaces of the polygon mirror 5, the main scanning incident angles α1 and α2 of the light beams L1 and L2, and the ratio D of the printing scanning angle to the total scanning angle among the characteristics. ing.
As shown in Tables 13 to 18, the optical scanning device according to the various embodiments also has all of the first to ninth conditions, that is, the conditional expressions (2), (4), (8a) or It can be seen that (8b), (12a) or (12b), (16a) or (16b), (17) and (19a) or (19b) are all satisfied.

[Image forming apparatus]
FIG. 5 shows a sub-scan sectional view of the main part of the color image forming apparatus 90 on which the optical scanning device according to the above embodiment is mounted.

The image forming apparatus 90 is a tandem type color image forming apparatus that records image information on each photosensitive drum surface as an image carrier by an optical scanning device.
The image forming apparatus 90 includes the optical scanning device 11 according to the above-described embodiment, the photosensitive drums 23, 24, 25, and 26 as image carriers, the developing devices 15, 16, 17, and 18, the conveyance belt 91, the printer controller 93, and the like. A fixing device 94 is provided.

  The image forming apparatus 90 receives R (red), G (green), and B (blue) color signals (code data) output from an external device 92 such as a personal computer. These color signals are converted into image data (dot data) of C (cyan), M (magenta), Y (yellow), and K (black) by a printer controller 93 in the image forming apparatus 90. These image data are input to the optical scanning device 11. The light scanning device 11 emits light beams 79, 80, 81, and 82 that are modulated according to each image data, and the light beams 79, 80, 81, and 82 emit the photosensitive drums 23, 24, The photosensitive surfaces 25 and 26 are scanned in the main scanning direction.

  The electrostatic latent images of the respective colors are formed on the photosensitive surfaces of the corresponding photosensitive drums 23, 24, 25, and 26 by the light beams 79, 80, 81, and 82 emitted from the optical scanning device 11 based on the respective image data. Is formed. Thereafter, the latent images of the respective colors are developed into the respective color toner images by the developing devices 15 to 18, the developed respective color toner images are transferred onto the transfer material by the transfer device, and the transferred toner image is fixed by the fixing device. One full color image is formed.

  Therefore, in the image forming apparatus 90, the optical scanning device 11 records image signals (image information) on the photosensitive surfaces of the photosensitive drums 23, 24, 25, and 26 corresponding to the colors C, M, Y, and K. Color images can be printed at high speed.

  As the external device 92, for example, a color image reading device including a CCD sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 90 constitute a color digital copying machine.

  Further, the recording density of the image forming apparatus according to the present embodiment is not particularly limited. However, considering that the higher the recording density is, the higher the image quality is required, the effect of the present invention is more exhibited when the optical scanning device according to the above-described embodiment is mounted in an image forming apparatus of 1200 dpi or more. Is done.

1 Light source 2 Aperture (incident optical system)
3 Condensing lens (incident optical system)
41, 42 Cylinder lens (incident optical system)
5 Polygon mirror (deflector)
61 First imaging lens (imaging optical system)
62, 63 Second imaging lens (imaging optical system)
71 surface to be scanned (first surface to be scanned)
72 surface to be scanned (second surface to be scanned)
100 Optical scanning device M1 Half mirror (incident optical system, splitting element)
M2, M3 Folding mirror (incident optical system)
M4, M5, M6 Folding mirror (imaging optical system)

Claims (10)

A deflector that deflects each of the first light beam and the second light beam to optically scan the effective area of the first scanned surface and the effective area of the second scanned surface in the main scanning direction;
An incident optical system for causing the first and second light beams to enter the deflector;
An imaging optical system for guiding the first and second light beams deflected by the deflector to the first and second scanned surfaces;
With
The deflector includes N deflecting surfaces that rotate about a rotation axis parallel to the sub-scanning direction,
The incident optical system includes a splitting element that splits a light beam emitted from a light source into the first and second light beams,
In the main scanning section, the angles formed by the incident directions of the first and second light beams on the deflector and the optical axis of the imaging optical system are respectively α1 and α2, and the total scanning angle of the deflector. When the ratio of the effective scanning angle corresponding to the effective area is D,
α2 ≦ α1-2 × 360 / N × D
α2 ≧ α1-2 × 360 / N × (1-D)
An optical scanning device characterized by satisfying the following condition. α2 <(α1-360 / N × D) / 2
Or α2> (α1 + 360 / N × D) / 2
The optical scanning device according to claim 1, wherein: α2> 2 × α1 + 360 / N × D
Or α2 <2 × α1-360 / N × D
The optical scanning device according to claim 1, wherein: α2> 2 × α1-360 / N (2-D)
Or α2> 2 × α1-360 / N (2 + D)
The optical scanning device according to claim 1, wherein: α1> 360 / N × D
5. The optical scanning device according to claim 1, wherein: α2> 360 / N × D
Or α2 <-360 / N × D
The optical scanning device according to claim 1, wherein:   The angles β1 and β2 are different from each other when the angles formed between the incident direction of the first light flux and the second light flux on the deflector and the main scanning section are β1 and β2, respectively. The optical scanning device according to any one of claims 1 to 6. The angles formed between the incident direction of the first light beam and the second light beam on the deflector and the main scanning section are β1 and β2, respectively, and the marginal light beam of each of the first light beam and the second light beam. When the spread angles in the sub-scan section are NA1 and NA2, respectively.
| Β1 |> NA1
| Β2 |> NA2
The optical scanning device according to claim 1, wherein:   9. The optical scanning device according to claim 1, a developing device that develops an electrostatic latent image formed on the surface to be scanned by the optical scanning device as a toner image, and a developed toner image. An image forming apparatus comprising: a transfer device that transfers the toner image to a transfer material; and a fixing device that fixes the transferred toner image to the transfer material.   An optical scanning device according to claim 1, and a printer controller that converts code data output from an external device into an image signal and inputs the image signal to the optical scanning device. Image forming apparatus.

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