JPH0675973B2 - Image recorder - Google Patents

Description

The present invention relates to an image recording apparatus having a mechanism for exposing a light beam modulated by an image signal to a light receiving surface to perform exposure. There is a laser printer, for example, as a recording device that records an image signal read by an image reading device or created by a computer or the like on a paper surface by using optical means. A laser printer guides a light beam modulated by an image signal to an exposure unit having a light receiving surface made of a photoconductor or the like, scans the light beam to form an electrostatic latent image, and then performs development, transfer, fixing, and the like. .

“Prior Art” FIG. 11 shows a mechanism of a laser printer that guides a light beam onto a light receiving surface and scans the light beam.

The apparatus shown in FIG. 1 includes a signal source 1 that stores an image signal read by a reading device (not shown), a light source 2 that emits a light beam modulated by the image signal, a collimator 4 that guides the light beam 3, and a cylinder. The lens 5, the rotary polygon mirror 6, the f-θ lens 7 and the cylinder lens 8, and the photosensitive drum 9 that receives the light beam on the outer peripheral surface and forms an electrostatic latent image.
It consists of and.

The light source 2 directly modulates the laser beam by the drive circuit 1 when the image signal is a binarized signal of white or black dots, for example. The light beam 3 emitted from the light source 2 is made into a beam having an oval cross section by the collimator 4 and the cylinder lens 5, and is incident on the reflecting surface 11 of the rotary polygon mirror 6.

The light beam 3 is then fed to the f-θ lens 7 and the cylinder lens 8.
Is narrowed to a narrow beam by the light receiving surface 10 of the photosensitive drum 9.
Incident on. When the rotary polygon mirror 6 rotates in the direction of arrow 12, the light beam 3 is repeatedly scanned from the broken line 13 to the broken line 14 in the direction parallel to the direction of the rotation axis 16 of the photosensitive drum 9. When the light beam 3 crosses the scanning start position sensor 17, an image signal is output from the signal source 1 at a predetermined timing, the light beam is scanned on the light receiving surface 10 of the photosensitive drum 9, and an image signal for one line is output during this period. Is completed.

"Problems to be Solved by the Invention" FIGS. 12 (1) and 12 (2) are front views of the reflecting surface 11 of the rotary polygon mirror 6 shown in FIG. As shown in this figure, the light beam 3 is converged on an oval spot 21 and is incident on the reflecting surface 11 of the rotary polygon mirror 6. The spot 21 moves in the direction of arrow 22 as the rotary polygon mirror 6 rotates. The light beam forming the spot 21 is finally focused on one point by a lens or the like and is applied to the photosensitive drum 9. Therefore, as shown in FIG. When it sticks out, the amount of light is halved. In such a case, since the light beam is not suitable for forming a latent image, the light beam is scanned in the range of broken lines 13 to 14 in FIG. 11 and only the intermediate portion is irradiated to the photosensitive drum for use. As shown in FIG. 12 (1), the actually effective spot moving distance l of the light beam is about one half of the width L of the reflecting surface in the direction perpendicular to the rotation axis of the rotary polygon mirror. Is the reality.

As described above, the conventional image recording apparatus has a problem that the light source is effectively used for image signal transmission only for about half the time during which the light source outputs the light. In addition, in order to increase the speed of this type of device, it is necessary to increase the rotation speed of the rotary polygon mirror or increase its radius, but it is necessary to increase the size of the device and increase wind loss during rotation. There was also a problem. Moreover,
Large polygon mirrors are not easy to manufacture and lead to increased costs.

On the other hand, as shown in FIG. 13, the width of the light beam is made sufficiently wide so that the light beam is always illuminated over the entire width of the reflection surface while the reflection surface of the rotating polygon mirror scans this light beam. Methods for forming spots have also been developed. This has the advantage that the spot area of the light beam reflected from the start to the end of scanning does not change.

However, for this purpose, it is necessary to widen the width of the light beam and increase the output of the light source. If the width of the light beam is too wide, the light source and its power source become large in size, which causes a cost increase.

The present invention has been made in view of the above points, and has an object to provide an image recording apparatus that efficiently guides a light beam output from a light source to an exposure unit and speeds up scanning. It is a thing.

"Means for Solving Problems" An image recording apparatus of the present invention includes a light source that emits a light beam modulated by an image signal, a light beam deflecting unit that switches the optical path of the light beam, and a light beam that is received. The exposure unit has a light receiving surface and a light beam scanning unit that guides a light beam onto the light receiving surface of the exposure unit and scans line by line. Rotating polygon mirrors each having a rotation axis in its part and having the same number of reflecting surfaces for reflecting a light beam on its outer peripheral surface have their rotation axes aligned with each other, and one ridge line parallel to the rotation axis forms one line in the rotation direction. The light beam deflector guides the light beam so that it converges within the reflecting surface of the rotating polygon mirror and is laminated in a predetermined order on the reflecting surface of the rotating polygon mirror. Light beams are incident line by line. It is characterized by switching the optical path of the lie.

Further, the image recording apparatus of the present invention includes a light source that emits a light beam modulated by an image signal, a light beam deflecting unit that switches the optical path of the light beam, and an exposure unit that receives the light beam on the light receiving surface. , A light beam scanning unit that guides a light beam onto the light-receiving surface of the exposure unit and scans line by line. The light beam scanning unit has a polygonal columnar outer shape and has a rotation axis at its shaft portion. Rotating polygon mirrors having the same number of reflecting surfaces that reflect light beams on their surfaces match their rotation axes with each other and shift the ridges parallel to the rotation axis by the angle required for scanning line by line in the rotation direction. The light beam diverting section irradiates the reflecting surface of the rotating polygon mirror with a light beam having a width wider than the width in the direction perpendicular to the rotation axis, and the reflecting surface of each rotating polygon mirror. The light beam of each line illuminates in a predetermined order. It is characterized by sequentially switching a direction parallel to the rotational axis of the optical path to be.

In any of the above image recording apparatuses, the following embodiments are preferable.

The light beam scanning unit may be provided with a unidirectional focusing optical element so that the reflecting surface of each rotary polygon mirror and the light receiving surface of the exposure unit are optically conjugate with each other in the scanning direction of the light beam.

The light beam deflecting unit may be provided with a deflector that divides the light beam into a plurality of optical paths and a shutter that allows passage of only the light beam passing through any one of these optical paths.

It is preferable that the light beam diverting portion is provided with an ultrasonic light modulator for making the light beam incident and a switching means for changing the diffraction angle.

[Operation] In the image recording apparatus of the present invention, the light beam is emitted to the reflecting surfaces of the plurality of rotary polygon mirrors in a predetermined order with its optical path switched for each scanning line. As a result, the scanning of the light beam is switched in the shortest time. Moreover, the protrusion of the spot from the reflecting surface can be reduced, and the light beam can be effectively guided to the exposure unit.

Further, in the case of the method of making the spot width wider than the width of the reflecting surface, the minimum necessary spot width can be made narrower than that of the conventional method, and the output of the light source can be suppressed low.

[Embodiment] FIG. 1 is a schematic configuration diagram showing an embodiment of an image recording apparatus of the present invention.

This image recording apparatus comprises a signal source 1, a light source 2, a light beam changing section 31, an exposure section 32 and a light beam scanning section 33.

The signal source 1 and the light source 2 are the same as those provided in the conventional image recording apparatus described in FIG. The light beam 3 is a semiconductor laser 34 (or a gas laser and a light modulator, etc.)
Is output from the image signal 36 after being modulated.

In the light beam changing section 31, as shown in FIG.
The light beam 3 is converted into two optical paths 4 by a deflector 41 including a pair of prisms 38 and 39 having a beam splitting function.
Divided into 3 and 44. Then, only the light beam passing through the predetermined optical path passes through one of the shutters 45 and 46, passes through the cylinder lens 47, and is irradiated onto the light beam scanning unit 33. At this time, the light beam 3 is converged by the cylinder lens 47 into a beam having an oval cross section.

The light beam scanning unit 33, as shown in FIG. 1 and FIG.
For example, it is composed of two rotary polygon mirrors 51, 52, an f-θ lens 53, and a cylinder lens 54. Rotating polygon mirrors 51, 52
Has a polygonal columnar outer shape, and has a rotating shaft 55 on its shaft portion and reflection surfaces 57, 58 for reflecting the light beam 3 on the outer peripheral portion. The two rotary polygon mirrors 51, 52 are laminated by shifting a ridge line 59 parallel to the rotation axis 55 thereof by a predetermined angle in the rotation direction. In the case of this embodiment, the ridgeline 59 of one rotary polygonal mirror 51 is arranged so as to be in the center of the reflecting surface 58 of the other rotary polygonal mirror 52, and the intervals between the ridgelines 59 are constant. The f-θ lens 53 corrects the image forming position of the beam because the light receiving surface 10 of the light receiving drum 9 is a flat surface, while the image forming surface of the scanned light beam 3 has an arc shape. It is a known lens for correcting the scanning position with respect to the f-θ characteristic. Further, in the image recording apparatus of the present invention, the optical paths of the light beams are switched, so that, for example, as shown in FIG. 3, the light beams passing through two different optical paths are respectively imaged on the same light receiving surface. Two cylinder lenses 47,
54 is provided. In FIG. 3, the same parts as those in FIGS. 1 and 2 are designated by the same reference numerals, and the description thereof will be omitted.

The exposure section 32 is composed of the same photosensitive drum 9 as described in FIG. In the embodiment shown in FIG. 1, two light beam sensors 61 and 62 are provided on both sides of the photosensitive drum in the axial direction. One light beam sensor 61 detects the scanning start timing of the light beam on the photosensitive drum, and the other light beam sensor 62 detects the scanning end. Light beam sensor 61
Is sent to an image signal output circuit (not shown) or the like for processing. The output of the light beam sensor 62 is sent to the optical path switching control circuit 63 provided in the light beam changing section 31.

The image recording apparatus described above operates as follows.

The light beam 3 reflected from the light source is split into two optical paths 43 and 44 by the right-angle prisms 38 and 39 of the light beam changing portion 31. Then, first, one shutter 45 is closed and the other shutter 46 is opened, and the light beam is guided from one optical path 44 to the reflecting surface 58 of the first rotary polygon mirror 52. This light beam is focused by a cylinder lens 47 into an elliptical spot of a size that converges on this reflecting surface. In FIG.
When the positions of the spots of the light beam 3 are represented as S _{1 to} S ₆ , the spots move from the positions S ₁ to S ₂ as the rotary polygon mirror 52 rotates.
Move to. At this time, the light beam is scanned from one side to the other side of the photosensitive drum 9, and the light beam sensor 61 detects the start of scanning and the light beam sensor 62 detects the end of scanning. When detecting the end of scanning, the optical path switching circuit 63 closes the shutter 45 and opens the shutter 44 to switch the optical path of the light beam 3.
This moves the spot from position S ₂ to position S ₃ ,
The photosensitive drum 9 is again scanned from one side to the other. In this way, the optical paths are switched in sequence, and the spot starts from S _1.
Move to S ₆ one after another.

FIG. 4 is a view in which two rotary polygon mirrors 71 and 72 having a square cross section are laminated, and a top view thereof is shown in FIG. The light beam is scanned while the position of the spot shifts in the order of S ₁ , S _2, ... S _6, and the same operation as that of the regular octagonal rotating polygon mirror as shown in FIG. 6 is performed. In the case of the present embodiment, since the spot of the light beam does not always protrude from the reflecting surface, the front surface of this reflecting surface can be effectively used. Therefore, the effective exposure rate of the scanning beam, that is, the effective scanning rate is increased to nearly 100%.

FIG. 7 shows an example in which three rotary polygon mirrors 74 are laminated, and the movement of the spot by switching the optical path is as shown by the broken line 81.
For example, as shown in FIG. 8, a rotating polygon mirror 74 having a square cross section
If four layers are laminated, it will have the same function as a mirror having 16 reflecting surfaces. At this time, the ridge lines 59 of each rotary polygon mirror are arranged at equal intervals in the circumferential direction. This makes it possible to provide a light beam scanning unit having a small radius but a high effective scanning rate and capable of high-speed scanning.

FIG. 9 shows a part of an octagonal rotary polygon mirror 74 having the same function as that of FIG. 5 on the same scale as that of FIG. 5, but the light beam irradiated on the reflecting surface is , In order to always hit the full width of the reflective surface, at least the width W ₁ shown in the figure
Need. However, in the case of FIG. 5, the minimum beam width W ₀ may be about two-thirds of the beam width W ₁ . As described above, according to the present invention, it is possible to economically irradiate the light energy even in the case of the method of irradiating the reflecting surface with the light beam having the wide beam width.

In addition, in the present invention, the deflector of the light beam deflector is not limited to the one in the embodiment, and an electric field is applied to an isotropic crystal or a piezoelectric crystal to cause birefringence in transmitted light to switch its optical path. Alternatively, as shown in FIG. 10, a high-frequency electric field 79 may be applied to propagate the ultrasonic wave to the medium 78, and the interaction between the ultrasonic wave and the light may diffract the light to obtain various optical paths. . At this time, two or more kinds of high-frequency electric fields to be applied to the crystal are prepared, and the diffraction angle (Bragg angle) θ changes if the switching is performed, so that the optical path may be switched by this. The lug angle θ is obtained by θ = λf / 2V (where λ is the wavelength of the light beam, f is the wavelength of the high frequency applied to the piezoelectric crystal, and V is the speed of sound of the ultrasonic wave in the medium).

Further, the light beam scanning unit 33 is preferably provided with a unidirectional focusing optical element 54 so that the reflecting surface of each rotary polygon mirror and the light receiving surface of the exposure unit are optically conjugate in the scanning direction of the light beam. In the embodiment of FIG. 3, the f-θ lens 53 is a cylinder.
54 and 54 form this unidirectional focusing optical element. By doing so, even if the parallelism of the reflecting surface of each rotating polygon mirror with respect to its rotation axis varies, it is possible to prevent the variation of the image forming position of the light beam on the light receiving surface.

Further, the scanning end detection for switching the scanning of the light beam may be performed by counting the pulse of the power supply supplied to the sensor for detecting the rotation angle of the rotary polygon mirror or the rotary drive motor of the rotary polygon mirror. . Further, a mark attached to the rotary polygon mirror may be read or a timer may be separately provided.

[Advantages of the Invention] The image recording apparatus of the present invention described above can speed up the scanning of the light beam when reproducing the image signal in the image recording apparatus, and can prevent wasteful consumption of light energy. . Further, since the plurality of rotary polygon mirrors are switched for each scanning line, it is possible to configure a scanning unit having a small diameter but a function equivalent to that of a large diameter rotary polygon mirror. Therefore, the load on the rotation driving motor of the rotary polygon mirror can be reduced, and the device can be downsized.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an image recording apparatus of the present invention, FIG. 2 is a perspective view of a main part thereof, FIG. 3 is an explanatory view of its optical path, and FIGS. 4 and 7 show a rotary polygon mirror. FIG. 5, FIG. 6, FIG. 8, FIG. 8 and FIG. 9 are explanatory views of their operation, and FIG. 10 is a perspective view of a modification of the main part of the light beam deflecting portion.
FIG. 11 is a schematic configuration diagram showing an embodiment of a conventional image recording apparatus,
12 and 13 are explanatory diagrams of the operation. 2 ... Light source, 3 ... Light beam, 31 ... Light beam changing section, 32 ... Exposure section, 33 ... Light beam scanning section, 41 ... Deflection device, 45, 46 ... Shutter, 51, 52 …… Rotating polygon mirror, 54 …… One-way focusing optics.

Claims (8)

[Claims] 1. A light source that emits a light beam modulated by an image signal, a light beam redirecting unit that switches the optical path of the light beam, an exposure unit that receives the light beam on a light-receiving surface, and this exposure. A light beam scanning unit that guides the light beam onto the light receiving surface of the scanning unit and scans it line by line. The light beam scanning unit has a polygonal outer shape and has a rotation axis at its shaft portion and an outer peripheral surface. Rotating polygonal mirrors having the same number of reflecting surfaces that reflect the light beam have their rotation axes aligned with each other, and a ridge line parallel to the rotation axis is shifted in the rotation direction by an angle required for scanning line by line. The light beam diverting section guides the light beam so as to be converged within the reflecting surface of the rotating polygon mirror, and guides the light of each line on the reflecting surface of the rotating polygon mirror in a predetermined order. So that the beam is incident The image recording apparatus characterized by switching the road. 2. A unidirectional focusing optical element is provided in the light beam scanning section so that the reflecting surface of each rotary polygon mirror and the light receiving surface of the exposure section are optically conjugate in the scanning direction of the light beam. The image recording apparatus according to claim 1, which is characterized in that. 3. The light beam diverting section is provided with a diverter for dividing the light beam into a plurality of light paths and a shutter for allowing only the light beam passing through any one of these light paths. The image recording apparatus according to claim 1 or 2, characterized in that 4. An ultrasonic wave optical modulator for injecting a light beam and a switching means for changing the diffraction angle are provided in the light beam diverting section.
The image recording apparatus according to item 2 or item 2. 5. A light source that emits a light beam modulated by an image signal, a light beam redirecting unit that switches the optical path of the light beam, an exposure unit that receives the light beam on a light receiving surface, and this exposure. A light beam scanning unit that guides the light beam onto the light receiving surface of the scanning unit and scans it line by line. The light beam scanning unit has a polygonal outer shape and has a rotation axis at its shaft portion and an outer peripheral surface. Rotating polygonal mirrors having the same number of reflecting surfaces that reflect the light beam have their rotation axes aligned with each other, and a ridge line parallel to the rotation axis is shifted in the rotation direction by an angle required for scanning line by line. The light beam deflecting unit irradiates the reflecting surface of the rotary polygon mirror with a light beam having a width wider than the width in the direction perpendicular to the rotation axis of the rotary polygon mirror, and 1 on the reflective surface in a predetermined order
An image recording apparatus, wherein the optical path is sequentially switched in a direction parallel to the rotation axis so that a light beam for each line is irradiated. 6. A unidirectional focusing optical element is provided in the light beam scanning section so that the reflecting surface of each rotary polygon mirror and the light receiving surface of the exposure section are optically conjugate in the scanning direction of the light beam. An image recording apparatus according to claim 5, which is characterized in that. 7. The light beam diverting section is provided with a diverter that divides the light beam into a plurality of light paths and a shutter that allows passage of only the light beam passing through any one of these light paths. The image recording apparatus according to claim 5 or 6, characterized in that 8. An ultrasonic wave optical modulator for making a light beam incident and a switching means for changing the diffraction angle are provided at the light beam diverting portion. The image recording device according to item 6 or 6.