JP2012150153A - Optical scanner and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner in conformity with a tandem system, capable of preventing return light, and speedily outputting an excellent image, while reducing the number of light sources.SOLUTION: The optical scanner comprises: an optical deflection element for deflecting/reflecting a light beam radiated from a light source; and beam bifurcating means which is provided on an upstream side in a light beam traveling direction, of the optical deflection element, and makes an incident light beam which is linearly polarized light, branch upward and downward. Between a half prism 4 serving as the beam bifurcating means and the optical deflection element, a linear polarizer 90 and a λ/4 plate 91 for converting the linearly polarized light to circularly polarized light are arranged in this order in the light beam traveling direction.

Description

  The present invention relates to an optical scanning device that forms an electrostatic latent image on an image carrier, a copying machine having the optical scanning device, a printer, a facsimile, a plotter, and an image forming device that includes at least one of them. Relates to the device.

In electrophotographic image forming apparatuses used in laser printers, digital copying machines, plain paper fax machines, etc., colorization and speeding up have progressed, and tandem image forming apparatuses having a plurality of (usually four) photoreceptors have become widespread. Yes.
As a color electrophotographic image forming apparatus, there is a method in which only one photoconductor is provided and the photoconductor is rotated by the number of colors (4 colors, one drum needs to be rotated four times), but productivity is high. Inferior to On the other hand, in the case of the tandem method, the number of light sources inevitably increases, and accordingly, the number of parts increases, color shift due to wavelength difference between a plurality of light sources, and cost increase.
Further, deterioration of the semiconductor laser is cited as a cause of the failure of the writing unit. As the number of light sources increases, the probability of failure increases and the recyclability deteriorates.

In view of this, there is an example in which a device that does not increase the number of light sources is made while being a tandem method (see Patent Document 1).
In this example, a light beam from a common light source is branched up and down, and the light beam is guided to different scanning surfaces by using polygon mirrors that are stacked in two stages with a phase shift. (See FIG. 1).
In the method of Patent Document 1, when the upper light beam scans the surface to be scanned, the incident angle of the lower light beam to the reflecting mirror may be 0, and the reflecting surface of the reflecting mirror is the light source. Since it faces the direction, there is a problem that the reflected light beam returns to the light source and the stability of the light output is remarkably lowered.
As a method for solving this problem, there is a method as described in Patent Document 2. In this example, the polarization direction of the light beam incident on the polarization beam splitter is changed by the liquid crystal element, and the light beam is prohibited from being branched to the lower stage while the upper light beam is scanning the surface to be scanned. Have been devised.

  In the method of Patent Document 2, a liquid crystal element and a polarizing beam splitter are required, and the optical system layout on the front side (upstream side in the beam traveling direction) of the optical deflection element (optical deflector) becomes complicated. In addition, the transmission axis of the liquid crystal element and the transmission axis / reflection axis of the polarizing beam splitter need to be matched with high accuracy, and adjustment thereof is difficult.

  The present invention has been made in view of such circumstances, and in an optical scanning device compatible with a tandem method, it is possible to prevent return light while reducing the number of light sources, and to provide a high-speed and good image output. The main purpose is provision.

  In order to achieve the above object, the invention according to claim 1 is provided in two upper and lower layers, deflects and reflects a light beam emitted from a light source, and upstream of the light beam traveling direction of the light deflection element. And a beam branching unit for vertically splitting an incident light beam of linearly polarized light between the beam branching unit and the light deflection element in order in the direction of travel of the light beam. A polarizer and a λ / 4 plate that converts linearly polarized light into circularly polarized light are arranged.

According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the optical deflection element has a configuration in which regular polygonal columns having N reflective surfaces are stacked in two upper and lower layers. The regular polygonal columns are characterized by being out of phase with each other by 180 ° ÷ N.
According to a third aspect of the present invention, in the optical scanning device according to the first or second aspect, a plurality of light beams are incident on the beam branching unit.
According to a fourth aspect of the present invention, there is provided an image forming unit for forming a latent image by performing optical scanning with a light scanning device on a photosensitive image carrier and visualizing the latent image with a developing unit. In the image forming apparatus having one or more, at least one of the optical scanning devices according to any one of claims 1 to 3 is used as the optical scanning device.

  According to the present invention, it is possible to prevent return light while reducing the number of light sources, and to realize good image output at high speed.

1 is a perspective view showing a schematic configuration of an optical scanning device according to an embodiment of the present invention. It is a sub-scanning sectional view of a beam branching means part. It is a top view for demonstrating the optical scanning by a polygon mirror, (a) is a figure which shows the state scanned with the upper stage mirror, (b) is a figure which shows the state scanned with the lower stage mirror. It is a timing chart of exposure for multiple colors. It is a timing chart for making exposure differ according to a color. It is a figure for demonstrating the scanning angle of a polygon mirror. 1 is a schematic configuration diagram of an image forming apparatus having an optical scanning device.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram showing a configuration of an optical scanning device 20 according to the present embodiment. In the figure, reference numeral 1 is a semiconductor laser as a light source, 3 is a coupling lens, 4 is a polarization beam splitter as a beam branching means, 5a and 5b are cylindrical lenses, 6 is soundproof glass, and 7 is an optical deflecting element (optical deflector). ), 8 is a first scanning lens (fθ lens), 9 is a folding mirror, 10 is a second scanning lens (toroidal lens), 11 is a photoreceptor as a surface to be scanned, and 12 is an aperture stop (aperture). Respectively.

The divergent light beam emitted from the semiconductor laser 1 is converted by the coupling lens 3 into a weak convergent light beam, a parallel light beam, or a weak divergent light beam.
The light beam exiting the coupling lens 3 passes through the aperture stop 12 for stabilizing the beam diameter on the scanned surface and enters the beam branching unit 4.
The light beam incident on the beam branching means 4 is split up and down, and the light beams emitted from the beam branching means 4 become one light beam at the top and bottom.
The light beam emitted from the beam branching means 4 is converted into a line image that is long in the main scanning direction in the vicinity of the deflection reflection surface of the light deflection element 7 by the cylindrical lenses 5a and 5b arranged vertically.

In the light deflection element 7, single polygon mirrors 7a and 7b are concentrically arranged on the upper and lower sides, respectively, and the rotation direction angles (angles in the main scanning plane) are shifted from each other.
Both polygon mirrors have the same shape, and in principle consist of arbitrary polygons (polygons with thicknesses in the vertical direction = polygonal cylinders), and the other has an angle that divides the central angle of one side of one polygon into approximately two equal parts. The polygon vertices are overlaid so that they correspond.
When looking at the vertices of the opposing polygon that are adjacent to each other in the clockwise direction from the vertices of each polygon, the central angles for the vertices between the vertices are φ and φ ′ (where 0 <φ ≦ φ ′). For example, if both are symmetrically arranged with respect to an arbitrary vertex, φ = φ ′.
In practice, a four-sided polygon mirror is the easiest to use, and here, the four-sided polygon mirror is set to φ = φ ′ = 45 °. These φ and φ ′ are referred to as deviation angles.

The upper and lower polygon mirrors 7a and 7b may be integrally formed or may be assembled separately.
In general, the shift angle φ is φ = (360 ° ÷ M) / 2, that is, 180 ° ÷ M, where M is the number of faces of the polygon mirror when both polygon mirrors are evenly shifted.
However, when the shift is not uniform, when the smaller shift angle is φ, the larger shift angle φ ′ is φ ′ = 360 ° ÷ M−φ.

FIG. 3 is a diagram for explaining optical scanning by the upper and lower two-layer polygon mirrors. In the figure, reference numeral 14 denotes a light shielding member.
As shown in the figure, when the upper light beam from the common light source is scanning the photoconductor 11a as the surface to be scanned, the lower light beam prevents the light beam from reaching the surface to be scanned. Is shielded by the light shielding member 14.
Further, when the lower light beam from the common light source is scanning the photoconductor 11b different from the upper light beam, the upper light beam is prevented from reaching the surface to be scanned.
Further, when the modulation drive is also shifted in the upper and lower stages and the photosensitive member 11a corresponding to the upper stage is scanned, the light source is modulated and driven based on the image information of the color (for example, black) corresponding to the upper stage, When scanning the photoreceptor 11b corresponding to the lower stage, the light source is modulated based on image information of a color (for example, magenta) corresponding to the lower stage.

FIG. 4 is a timing chart of exposure for a plurality of colors. In the figure, the vertical axis represents the amount of light and the horizontal axis represents time.
A time chart in the case where black and magenta exposure is performed with a common light source and all the lights are turned on in the effective scanning region is shown in FIG. A solid line indicates a portion corresponding to black, and a dotted line indicates a portion corresponding to magenta.
The writing start timing in black and magenta is determined by detecting the scanning beam with the synchronous light receiving means arranged outside the effective scanning width. Although the synchronous light receiving means is not shown, a photodiode is usually used.
FIG. 5 is a timing chart for varying the exposure amount depending on the color. In FIG. 4, the light amounts in the black and magenta regions are set to be the same. However, since the transmittance and reflectance of the optical element are actually different, if the light amount of the light source is the same, the photosensitive member The light amount of the light beam that reaches is different.
Therefore, as shown in FIG. 5, when the different photoconductor surfaces are scanned, the light amounts set on the different photoconductor surfaces can be made equal by making the set light amounts different from each other.
The plurality of beams emitted from the light source 1 shown in FIG. 1 form one scanning line in one scanning on two different photosensitive members.

FIG. 7 is a diagram showing a basic configuration of the multicolor image forming apparatus.
In the figure, reference numeral 31 denotes a photosensitive member corresponding to reference numeral 11 in FIG. 1, 32 denotes a charger, 34 denotes a developing device (developing means), 35 denotes a cleaning means, 36 denotes a transfer charging means, 39 denotes a transfer belt, and 40 denotes A fixing unit 20 indicates a writing unit.
Y, M, C, and K represent image colors, and indicate yellow, magenta, cyan, and black, respectively.
The photoreceptors 31Y, 31M, 31C, and 31K rotate in the direction of the arrow, and in order of rotation, the chargers 32Y, 32M, 32C, and 32K, the developing devices 34Y, 34M, 34C, and 34K, the transfer charging units 36Y, 36M, 36C and 36K and cleaning means 35Y, 35M, 35C and 35K are provided.

The chargers 32Y, 32M, 32C, and 32K are charging members that constitute a charging device for uniformly charging the surface of the photoreceptor.
The surface of the photosensitive member between the charger and the developing devices 34Y, 34M, 34C, and 34K is irradiated with a beam by the optical scanning device 20, and an electrostatic latent image is formed on the photosensitive member.
Then, based on the electrostatic latent image, a toner image is formed on the surface of the photoreceptor by the developing device.
Further, the transfer toner images of the respective colors are sequentially transferred onto the recording paper (not shown) conveyed on the transfer belt 39 by the transfer charging means 36Y, 36M, 36C, and 36K, and finally are transferred onto the recording paper (not shown) by the fixing means 40. The image is fixed.

The implementation data of the optical system is shown below.
Light source wavelength: 655 nm
Coupling lens focal length: 15mm
Coupling action: Collimating action Polygon mirror deflecting reflection surface number: 4, inscribed circle radius: 7mm, vertical angle difference φ is 45 °
Average incident angle α = 29 ° to the reflector
A cylindrical lens having a focal length of 110 mm is disposed between the polarizing beam splitter and the light deflection element, and forms a long line image in the main scanning direction in the vicinity of the reflecting mirror.

Lens data after the optical deflector is shown below.
The first surface of the first scanning lens and both surfaces of the second scanning lens are expressed by the following equations (1) and (2).
[Main scanning non-arc type]
The surface shape in the main scanning plane is a non-arc shape, the paraxial radius of curvature in the main scanning plane on the optical axis is R _m , the distance in the main scanning direction from the optical axis is Y, the cone constant is K, high When the next coefficients are A ₁ , A ₂ , A ₃ , A ₄ , A ₅ , A ₆ ,..., The depth in the optical axis direction is X and is expressed by the following polynomial.

Here, when numerical values other than zero are substituted for odd-order coefficients A ₁ , A ₃ , A ₅ ,..., They have an asymmetric shape in the main scanning direction.
[Sub-scanning curvature formula]
An expression for changing the sub-scanning curvature according to the main scanning direction is shown by (2).

Here, when a value other than zero is substituted for B's odd power coefficients B ₁ , B ₃ , B ₅ ,..., The radius of curvature of sub-scanning becomes asymmetric in the main scanning direction.
Further, the second surface of the first scanning lens is a rotationally symmetric aspherical surface and is expressed by the following equation.
[Rotationally symmetric aspheric surface]
The paraxial radius of curvature in the optical axis is R, the distance in the main scanning direction from the optical axis is Y, the cone constant is K, and the higher order coefficients are A ₁ , A ₂ , A ₃ , A ₄ , A ₅ , A ₆ , ..., the depth in the optical axis direction is represented by X and is expressed by the following polynomial.

<Shape of the first surface of the first scanning lens>
R _m = −279.9
R _s = −61
K = -2.900,000 × 10
A ₄ = 1.755765 × 10 ⁻⁷
A ₆ = −5.491789 × 10 ⁻¹¹
A ₈ = 1.087700 × 10 ⁻¹⁴
A ₁₀ = −3.183245 × 10 ⁻¹⁹
A ₁₂ = −2.635276 × 10 ⁻²⁴
B ₁ = −2.066347 × 10 ⁻⁶
B ₂ = 5.727737 × 10 ⁻⁶
B ₃ = 3.152201 × 10 ⁻⁸
B ₄ = 2.280241 × 10 ⁻⁹
B ₅ = −3.729852 × 10 ⁻¹¹
B ₆ = −3.283274 × 10 ⁻¹²
B ₇ = 1.765590 × ^{10 -14}
B ₈ = 1.372995 × 10 ⁻¹⁵
B ₉ = −2.889722 × 10 ⁻¹⁸
B ₁₀ = −1.984531 × 10 ⁻¹⁹

<Shape of the second surface of the first scanning lens>
R = −83.6
K = −0.549157
A ₄ = 2.748446 × 10 ⁻⁷
A ₆ = −4.502346 × 10 ⁻¹²
A ₈ = −7.336645 × 10 ⁻¹⁵
A ₁₀ = 1.803003 × 10 ⁻¹⁸
A ₁₂ = 2.727900 × 10 ⁻²³

<Shape of the first surface of the second scanning lens>
R _m = 6950
R _s = 110.9
K = 0.0000 × 10
A ₄ = 1.549648 × 10 ⁻⁸
A ₆ = 1.292741 × 10 ⁻¹⁴
A ₈ = −8.811446 × 10 ⁻¹⁸
A ₁₀ = −9.182312 × 10 ⁻²²
B ₁ = −9.593510 × 10 ⁻⁷
B ₂ = −2.135322 × 10 ⁻⁷
B ₃ = −8.079549 × 10 ⁻¹²
B ₄ = 2.390609 × ^{10 -12}
B ₅ = 2.881396 × 10 ⁻¹⁴
B ₆ = 3.693775 × 10 ⁻¹⁵
B ₇ = −3.28584 × 10 ⁻¹⁸
B ₈ = 1.814487 × 10 ⁻²⁰
B ₉ = 8.722085 × 10 ⁻²³
B ₁₀ = −1.3340807 × 10 ⁻²³

<Shape of the second surface of the second scanning lens>
R _m = 766
R _s = −68.22
K = 0.0000 × 10
A ₄ = −1.150396 × 10 ⁻⁷
A ₆ = 1.096926 × 10 ⁻¹¹
A ₈ = −6.5542135 × 10 ⁻¹⁶
A ₁₀ = 1.998481 × 10 ⁻²⁰
A ₁₂ = −2.411512 × 10 ⁻²⁵
B ₂ = 3.644079 × 10 ⁻⁷
B ₄ = −4.847051 × 10 ⁻¹³
B ₆ = −1.666159 × 10 ⁻¹⁶
B ₈ = 4.534859 × 10 ⁻¹⁹
B ₁₀ = −2.819319 × 10 ⁻²³

Further, the refractive indices of the scanning lenses at the used wavelength are all 1.52724.
The optical arrangement is shown below.
Distance d ₁ from the deflection surface to the first surface of the first scanning lens: 64 mm
Center wall thickness d ₂ of the first scanning lens: 22.6 mm
Distance d ₃ from the second surface of the first scanning lens to the first surface of the second scanning lens: 75.9 mm
Center thickness d ₄ of the second scanning lens: 4.9 mm
Distance d ₅ from the second surface of the second scanning lens to the surface to be scanned: 158.7 mm
In addition, a soundproof glass and a dustproof glass having a refractive index of 1.514 and a thickness of 1.9 mm are disposed, and the soundproof glass is inclined by 10 ° with respect to a direction parallel to the main scanning direction in the deflection rotation plane.
The dustproof glass is not shown, but is disposed between the second scanning lens and the surface to be scanned.
Further, FIG. 1 discloses only a diagram corresponding to two photoconductors, but scanning four photoconductors by disposing an optical system similar to the optical system illustrated with a polygon mirror interposed therebetween. be able to.

By the way, although the necessity of the light shielding member 14 was demonstrated in FIG. 3, this is not enough only with respect to light shielding. This will be described with reference to FIG.
FIG. 6 is a diagram for explaining the scanning angle of the polygon mirror. In the figure, symbol α represents the angle of incidence on the reflecting mirror in the effective scanning width, θ represents the angle of view including the synchronous light receiving means, and φ represents one angular deviation in the rotational direction of the reflecting mirrors at different stages (upper and lower stages). .
Normally, only light receiving means for detecting the light beam is provided prior to the light beam being exposed to the effective scan width. However, in order to obtain information for correcting the scan width magnification, the light is applied after the effective scan width is exposed. Sometimes a beam is detected. In this case, the angle of view includes the light beam reaching the light receiving means before the start of scanning and after the start of scanning.
In the figure, the light deflection element 7 rotates at a constant angular speed in the clockwise direction.

Now, specifically, the number of faces M of the light deflection element 7 is set to 4 and φ = 45 °.
First, in order to separate the light beam incident on the light deflection element 7 and the light beam corresponding to the angle of view θ within the deflection rotation plane, it is necessary to satisfy θ ÷ 2 <α (4).
Here, the light beam A in the figure is the light beam at the most peripheral angle of view on the scanning end side, and here it is a light beam deflected by the upper (hatched) reflecting mirror. At this time, it is necessary that the light beam A ′ emitted from the light source common to the upper light beam and reflected by the lower reflecting mirror does not expose the surface to be scanned.
In this case, the angle between the light beam A ′ and the light beam A is 90 °. In order to prevent the light beam A ′ from scanning the surface to be scanned, the effective width including the light beam A ′ until synchronization is set. Must be on the outside.
That is, α + θ ÷ 2 <90 ° (5) is required. At that time, the light beam may be blocked by the light blocking member 14 as shown in the drawing.

However, when image formation is performed with a width of 13 inches, the effective scanning width is 330 mm. If light receiving elements are arranged at both ends at positions of 3 mm on the outer side, it is necessary to scan with a 336 mm light beam.
When this is achieved by a scanning optical system with a focal length of 210 mm, the angle of view θ is 336 ÷ 210 = 1.6 = 91.7 °, and α <44.15 ° from equation (5). 4) The equation is not satisfied (45.85 °> 44.15 °).
Even if the focal length of the scanning optical system is set to be long and the expressions (4) and (5) are satisfied at the same time, the angle of view θ is not sufficient in the vicinity of 90 °. It is necessary to set α and θ in consideration of the layout of the lens 8 and the cylindrical lens 5.
In other words, as an actual problem, when the upper light beam is scanning the surface to be scanned, the incident angle of the lower light beam to the reflecting mirror may be 0, and the reflecting surface of the reflecting mirror may be in the direction of the light source. Therefore, the reflected light beam returns to the light source, and the stability of the light output is significantly reduced.

The measures of the present invention for solving this problem will be described below.
FIG. 2 is a sub-scan sectional view of the half prism 4. The half prism 4 functions as a beam splitting means, and is composed of a section 41 having a triangular cross section and a section 42 having a parallelogram shape.
The adhesive surface 4a of the portions 41 and 42 is a half mirror, and separates transmitted light and reflected light at a ratio of 1: 1. A surface 4b of the parallelogram portion 42 facing the bonding surface 4a is a total reflection surface and has a function of changing the direction.
Further, a linear polarizer 90 and a λ / 4 plate 91 are provided on the exit surface side of the half prism.
The light beam incident on the half prism 4 is linearly polarized light whose polarization direction matches the sub-scanning direction, and the transmission axis of the linear polarizer 90 also matches this direction.

The light beam incident on the half prism 4 is split into two upper and lower light beams while maintaining the polarization direction. However, the light beam is transmitted through the linear polarizer 90 without loss of light quantity and is converted into circularly polarized light by the λ / 4 plate 91. It enters the light deflecting means 7.
Here, if the return light from the light polarization means 7 is generated, the return light is transmitted through the λ / 4 plate 91 again, and is converted into linearly polarized light orthogonal to the incident light beam. The return light is completely cut by the linear polarizer 90 that will subsequently pass through.
The linear polarizer 90 and the λ / 4 plate 91 may be integrated and attached to the exit surface side of the half prism 4. In this way, there is an advantage that the layout can be made compact.

4 Half prism as beam splitting means 7 Optical deflecting element 20 Optical scanning device 31 Photosensitive body as image carrier 90 Linear polarizer 91 λ / 4 plate

JP 2006-284822 A JP 2008-164861 A

Claims (4)

A beam that is arranged in two upper and lower layers and deflects and reflects the light beam emitted from the light source, and a beam that is provided upstream of the light deflection element in the traveling direction of the light beam and branches the vertically polarized incident light beam up and down In an optical scanning device having branching means,
A linear polarizer and a λ / 4 plate for converting linearly polarized light into circularly polarized light are arranged between the beam branching means and the light deflecting element in order in the traveling direction of the light beam. Optical scanning device. The optical scanning device according to claim 1,
The light deflection element has a configuration in which regular polygonal prisms having N reflecting surfaces are stacked in two upper and lower layers, and the regular polygonal prisms are out of phase with each other by 180 ° / N. Optical scanning device. The optical scanning device according to claim 1 or 2,
An optical scanning device characterized in that a plurality of light beams are incident on the beam branching means. In an image forming apparatus having one or more image forming units for forming a latent image by performing optical scanning with an optical scanning device on a photosensitive image carrier and visualizing the latent image with a developing unit.
An image forming apparatus using one or more of the optical scanning devices according to claim 1 as the optical scanning device.

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