JP2903730B2 - Multi-beam raster scanner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam raster scanning apparatus which forms a plurality of latent images on a photoreceptor, and more particularly to a negative latent image and a beam irradiation in which a beam irradiation section becomes an image section. The present invention relates to an improved multi-beam raster scanning apparatus which is effective in a type in which a positive latent image serving as a background portion other than an image portion is formed.

[0002]

2. Description of the Related Art Conventionally, as an image recording apparatus such as a copying machine or a printer for recording a multi-color image while satisfying the demand for miniaturization and high speed, for example, an apparatus described in Japanese Patent Application Laid-Open No. 57-63565 is known. Already provided.

[0003] This is a device for recording a two-color image. A charger for charging the photosensitive drum, a first latent image writing laser, and a second latent image writing laser are provided around the photosensitive drum. The first and second developing units in which developers of different color toners are stored are disposed at the subsequent stage of the beam irradiation position, and a transfer unit for transferring a toner image to recording paper is disposed at the subsequent stage. It is arranged.

[0004] The image recording process of this type is as follows.
First, the surface of the photosensitive drum is charged in advance by a charging device, and then a first latent image is formed by a first latent image writing laser, and a first toner image is formed by a first developing device. Forming a second latent image with a second latent image writing laser, and forming a second toner image with a second developing device;
In the transfer device, each toner image carried on the photosensitive drum is collectively transferred to the recording paper side, but from the viewpoint of effectively preventing mixing and mixing of toners of each color, each toner is used as a toner of each color. For example, one having a different polarity is selected.For example, the first latent image (a negative latent image whose beam irradiator is an image portion) is reversely developed with one color toner, and the second latent image (a beam irradiator A so-called negative-positive developing method in which a positive latent image serving as a background portion other than the image portion is normally developed (see JP-A-55-137538).

[0005]

When the above-described negative / positive developing method is employed, the fog toner is applied to the background portion on the positive latent image side where the beam irradiation portion is the background portion other than the image portion. It is necessary to take care not to adhere to the image.On the other hand, on the negative latent image side where the beam irradiator is the image part, take care not to unnecessarily increase the line width of the image part in order to maintain good image quality. In consideration of these points, the spot diameter of the laser beam for the negative latent image on the photosensitive drum is sufficiently narrowed, and the spot diameter of the laser beam for the positive latent image on the photosensitive drum is reduced. Is preferably set to be larger than that for the negative latent image.

Under such a demand, as a conventional method of variably setting the spot diameter of each laser beam, for example, the lighting time of the laser beam is variably set for the spot diameter of the laser beam in the main scanning direction of the photosensitive drum. Regarding the spot diameter of the laser beam in the sub-scanning direction of the photosensitive drum, for example, the curvature of the cylindrical mirror for tilt correction of the polygon mirror disposed between the imaging lens and the photosensitive drum is made different. It is conceivable to cope with this by changing the width of the slit through which the irradiation laser beam passes.

However, in variably setting the spot diameter of the laser beam in the sub-scanning direction of the photosensitive drum,
In the case of the type using cylindrical mirrors with different specifications with different curvatures, the technical problem that the equipment cost is unnecessarily increased cannot be avoided, and in the type in which the slit width is variably set, the slit width is reduced. There is a technical problem that the loss of the laser beam on the side to be used increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problems, and it is intended to minimize the loss of the light quantity of an irradiation beam and to reduce the cost of the apparatus while reducing the cost of the positive latent image. An object of the present invention is to provide a multi-beam raster scanning apparatus capable of optimizing a spot diameter of a beam and a beam for a negative latent image on a photoconductor.

[0009]

That is, a multiple beam raster scanning apparatus according to the present invention, as shown in FIG. 1, comprises a negative latent image beam generating means for generating a beam Bn corresponding to an image portion to be developed. 1, a positive latent image beam generating means 2 for generating a beam Bp corresponding to a background portion other than the image portion to be developed, and a plurality of systems of beams Bn and Bp from each of the beam generating means 1 and 2. 3, beam deflection means 4 for deflecting and scanning over the main scanning direction, and a plurality of systems of beams Bn, Bp deflected by the beam deflection means 4 are imaged on respective main scanning line positions S1, S2 of the photoconductor 3. Imaging means 5 for beaming and beam deflecting means 4
And a deflection surface tilt correction means 6 interposed in the beam paths of a plurality of systems between the photoconductors 3 and correcting the tilt of the deflection surface of the beam deflection means 4, respectively. As means 6, the beams Bn, Bp
Have one-way converging optical members 7n and 7p of common specifications that converge only in one direction corresponding to the sub-scanning direction of the photoconductor 3;
The optical conditions Cn and Cp for the unidirectional focusing optical members 7n and 7p were changed so that the spot diameter of the negative latent image beam Bn in the sub-scanning direction was smaller than that of the positive latent image beam Bp. It is characterized by the following.

In such technical means, as each of the beam generating means 1 and 2, a semiconductor laser is used as long as it generates respective beams Bn and Bp based on an image signal corresponding to an image portion or a background portion. , Gas laser, etc. can be selected as appropriate, and are usually provided individually, but both are shared by one beam generating means such as separating a beam from one light source into a plurality of systems by a separating means such as an acousto-optic modulator. It may be designed so that

The beam deflecting means 4 may be a polygon mirror, a galvanomirror, etc., as long as it guides the beams Bn, Bp from the beam generating means 1, 2 to the respective scanning lines S1, S2 on the photosensitive member 3. It can be selected as appropriate. Also, the design of the imaging means 5 can be changed as appropriate, such as the lens shape and the number of lenses. Further, the beam deflecting means 4 and the imaging means 5 may be separately provided for each of the beams Bn and Bp, but from the viewpoint of reducing the cost and simplifying the apparatus, each beam Bn and Bp is used. It is preferable that the beam deflecting means 4 and the imaging means 5 are designed to be shared.

Further, as the one-way focusing optical members 7n and 7p, a cylindrical mirror, a cylindrical lens, and the like can be appropriately selected as long as they can correct the deflection surface tilt of the beam deflecting means 4 in a common specification.

The optical conditions Cn and Cp for the one-way focusing optical members 7n and 7p include the one-way focusing optical member 7n and 7p.
Beam incident angle to n, 7p, beam deflecting means 4 and photoconductor 3
And the conjugate positional relationship between the one-way focusing optical members 7n and 7p. At this time, the above optical conditions Cn, Cp
Are appropriately selected depending on how much the spot diameter of the irradiation beam is set.

[0014]

According to the technical means as described above, the beams Bn and Bp of a plurality of systems from the respective beam generating means 1 and 2 are combined with the beam deflecting means 4, the image forming means 5 and the unidirectional focusing optics of the common specification. Irradiation is performed on the photoconductor 3 via the members 7n and 7p.

At this time, the spot diameter of one of the beams Bn corresponding to the sub-scanning direction of the photosensitive member 3 has a one-way focusing optical member.
The spot diameter corresponding to the sub-scanning direction of the photosensitive member 3 of the other beam Bp is optimally determined by the optical condition Cp (Cn ≠ Cp) for the one-way focusing optical member 7p. You.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the accompanying drawings. FIG. 2 shows an embodiment of a two-color laser printer to which the present invention is applied. In FIG. 1, reference numeral 10 denotes a photosensitive drum, 11 denotes a charging corotron that charges the photosensitive drum 10 in advance, and 12 denotes a first latent image (the image portion potential is more absolute than the background portion potential) on the charged photosensitive drum 10. A laser scanning unit (hereinafter referred to as ROS [Raster Output Scanner]) that writes a second latent image (a low latent image), a second latent image (a positive latent image whose image portion potential is higher in absolute value than the background portion potential),
Reference numeral 13 denotes a first developing device of a magnetic brush developing system for reversal developing the first negative latent image written on the photosensitive drum 10 with, for example, black toner, and 14 denotes a second positive latent image written on the photosensitive drum 10. A second developing device 15 of a magnetic brush developing system for regularly developing the image with, for example, a red toner, before the transfer for removing the charge on the photosensitive drum 10 by aligning the polarity of the charge of each toner image on the photosensitive drum 10 A processing corotron, 16 is a transfer corotron for transferring the toner image on the photosensitive drum 10 to the recording paper 17, and 18 is a device for removing the charged charges on the recording paper 17 after the transfer process and peeling off the recording paper 17 electrostatically attracted to the photosensitive drum 10. Reference numeral 19 denotes a cleaner for removing residual toner on the photosensitive drum 10, and reference numeral 20 denotes a discharge lamp for removing residual charges on the photosensitive drum 10.

In this embodiment, the ROS 12 includes a first semiconductor laser 31 for writing a first latent image and a second semiconductor laser for writing a second latent image in a unit case 30. a laser 32 (the same rating as the first semiconductor laser 31), a collimator lens 33 for collimating the beam B _1, B ₂ from the semiconductor laser 31, the beam from the semiconductor lasers 31 and 32
A polygon mirror 35 for distributing B ₁ , B ₂ over the scanning range of the photosensitive drum 10 and a beam B ₁ , B ₂ distributed by the polygon mirror 35 form a linear locus corresponding to a scanning line on the photosensitive drum 10. Fθ lens 36 that corrects to draw,
A predetermined number of reflection mirrors 37 to 40 are provided in the optical paths of the passing beams B ₁ and B ₂ of the fθ lens 36 and reflect the beams B ₁ and B ₂ toward the respective scanning line positions of the photosensitive drum 10. Is stored in the positional relationship of. Reference numerals 51 and 52 denote optical windows 51 and 52 for sealing mounted on the light outlet of the unit case 30, respectively.

The reflection mirrors 38 and 40 are cylindrical mirrors for correcting the tilt of the polygon mirror 35. These reflection mirrors 38 and 40 have the same curvature but are common to the reflection mirrors 38 and 40. The optical conditions are different. More specifically, as shown in FIG. 3, the beam incident angles with respect to the reflecting mirrors 38 and 40 are θ ₁ and θ ₂ (≠ θ ₁ ), respectively, and the polygon mirror 35 and the reflecting mirrors 38 and 40 are The optical path lengths between a and c, and the optical path lengths between the scanning lines S1 and S2 of the photosensitive drum 10 and the reflection mirrors 38 and 40 are respectively b and c.
If d, the optical path length conjugate relationship on the reflection mirror 38 side (conjugate relationship with a, b) and the optical path length conjugate relationship on the reflection mirror 40 side (conjugate relationship with c, d) are set to be different, The spot diameters of the beams B ₁ and B ₂ in the sub-scanning direction of the photosensitive drum 10 are n ₁ and n ₂ (>
n ₁ ) has been adjusted. However, the entire optical path length a + b on the side of the reflecting mirror 38 and the entire optical path length c + d on the side of the reflecting mirror 40 are kept constant, and the respective beams B1 and B2 form an image in the main scanning direction of the photosensitive drum 20. The characteristics are set equal. In this example, θ ₁ = 48.3 °, θ ₂ = 47.
7 °, a = 203 mm, b = 132 mm, c = 193 mm, d = 142 mm.

In this embodiment, as shown in FIG. 3, the beam lighting time for one pixel of the drive circuit of the semiconductor lasers 31 and 32 is variably set, and the lighting time for one pixel on the semiconductor laser 32 side is set to the semiconductor laser. By making it longer than the laser 31 side, the beam diameters of the beams B ₁ and B _{2 in} the main scanning direction of the photosensitive drum 10 are adjusted to be set to m ₁ and m ₂ (> m ₁ ), respectively.

Next, an image recording process by the laser printer according to this embodiment will be described. First, the charger
At 11, the surface of the photosensitive drum 10 is uniformly charged to a predetermined potential (FIG.
a) Then, the first negative latent image Z ₁ (the potential difference between the image portion and the background portion) is formed on the photosensitive drum 10 by the beam B ₁ (irradiation light amount P (1)) from the first semiconductor laser 31. H ₁ ), and in the first developing unit 13, the negative latent image Z ₁ is reversely developed in a state where the developing bias V _B1 is applied to form a first toner image T _1.
(FIG.4b), after which the beam from the second semiconductor laser 32
A _second positive latent image is formed on the photosensitive drum 10 at B ₂ (irradiation light amount P (2)).
Z ₂ (the potential difference H ₂ <H ₁ between the image portion and the background portion) is formed, and the second latent developer 14 normalizes the positive latent image Z ₂ with the developing bias V _B2 applied. Develop the second toner image T ₂
(FIG. 4c), and further, the polarity of each toner image T ₁ , T ₂ is aligned by the pre-transfer treatment corotron 15 (FIG. 4d), and then each toner image T is transferred to the recording paper 17 side by the transfer corotron 16. _1, is obtained by the T ₂ so as to collectively transferred.

[0021] In such an image recording process, the spot diameter of the beams B ₁ to form the negative latent image Z ₁ is
(m ₁ , n ₁ ) is set to be sufficiently small, and the positive latent image Z ₂
Since the spot diameter of the beam B ₂ to form the set in those sufficiently larger than the spot diameter of the beams B ₁ for negative latent image (m _2, n _2), and the negative latent image Z ₁ Toner the line width of the image T ₁ is not to those unnecessarily thick, and it no adhering toner fog on the background portion of the toner image T ₂ of the positive latent image Z _2, of very good quality two-color images was gotten.

[0022]

As described above, according to the multi-beam raster scanning apparatus of the present invention, the unidirectional convergence as a deflection plane tilt correcting means can be achieved without unnecessarily narrowing the irradiation beam by the slit. By using an optical member, the spot diameter of the beam for the negative latent image can be set smaller than that of the beam for the positive latent image, minimizing the loss of light quantity of the irradiation beam and simplifying the device configuration. The quality of the visible image with respect to a plurality of systems of negative / positive latent images can be kept extremely high while achieving image quality.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a multi-beam raster scanning device according to the present invention.

FIG. 2 is a diagram illustrating an embodiment of a two-color laser printer to which the present invention is applied.

FIG. 3 is an explanatory diagram showing optical conditions for reflection mirrors 38 and 40 according to the embodiment.

FIG. 4 is an explanatory diagram illustrating an image recording process according to the embodiment.

[Explanation of symbols]

 1 Beam generating means for negative latent image 2 Beam generating means for positive latent image 3 Photoreceptor 4 Beam deflecting means 5 Imaging means 6 Deflection surface tilt correction means 7n Unidirectional focusing optical member 7p Unidirectional focusing optical member Cn Optical conditions Cp Optical condition 10 Photosensitive drum 31 Semiconductor laser 32 Semiconductor laser 35 Polygon mirror 36 fθ lens 38 Reflective mirror (cylindrical mirror) 40 Reflective mirror (cylindrical mirror)

Claims (1)

(57) [Claims] 1. A beam corresponding to an image area to be developed.
(Bn) for generating a negative latent image beam generating means (1), and a positive latent image beam generating means (2) for generating a beam (Bp) corresponding to a background portion other than the image portion to be developed, A plurality of beams (Bn, Bp) from each beam generating means (1, 2) are
(3) Beam deflecting means for deflecting and scanning over the main scanning direction
(4), a plurality of systems of beams (Bn, Bp) deflected by the beam deflecting means (4) are applied to each main scanning line position (S1,
S2), an image forming means (5) for image formation, and a beam deflecting means (4) and a photosensitive member (3). In the multi-beam raster scanning device provided with deflection surface tilt correction means (6) for correcting tilt, the deflection surface tilt correction means (6) includes a plurality of beams (Bn, Bp) of the photoconductor (3). One-way focusing optical member with common specifications that focuses in only one direction corresponding to the sub-scanning direction
(7n, 7p) so that the spot diameter in the sub-scanning direction of the negative latent image beam (Bn) on the photoreceptor (3) is smaller than that of the positive latent image beam (Bp). Direction focusing optical member (7n,
Multi-beam raster scanning device characterized by different optical conditions (Cn, Cp) for (7p)