JP2002116395A - Optical scanner and image forming device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical scanner suitable for high-definition printing by using multiple beams, and an image forming device using the same. SOLUTION: In this optical scanner, plural beams are deflected by a deflection means, and nearly the same area on a surface to be scanned is optically scanned by plural deflected beams successively so as to give multilevel light quantity to the surface to be scanned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device and an image forming apparatus using the same, and more particularly, to a scanning optical device (f.theta. Lens) which reflects and deflects a plurality of light beams emitted from a light source means by a polygon mirror as an optical deflector. The system is suitable for apparatuses such as a laser beam printer and a digital copying machine having an electrophotographic process, in which image information is recorded by sequentially optically scanning the same scanning line on the surface to be scanned through the system. .

[0002]

2. Description of the Related Art Conventionally, in an optical scanning apparatus such as a laser beam printer, a light beam emitted from a light source means such as a semiconductor laser after being modulated in accordance with an image signal is deflected by a deflecting means comprising, for example, a rotating polygon mirror (polygon mirror). The recording medium is periodically deflected, converged in the form of a spot on a photosensitive recording medium (photosensitive drum) surface by scanning optical means having fθ characteristics, and optically scans the recording medium surface to record an image.

In such an optical scanning apparatus, high-speed recording and high-resolution recording are demanded. In particular, in order to realize high-resolution recording, as an approach from the recording scanning optical system side, there is miniaturization of a recording image spot.

[0004] One method for this purpose is to shorten the wavelength of the laser or brighten the F number of the optical system. In addition, there is a method of obtaining a minute spot using a mask for controlling the phase of a light beam.

[0005]

Oscillation wavelengths of semiconductor lasers are currently being put to practical use in the range of 650 to 680 nm, and development has recently progressed to the 400 nm range. However, when the laser wavelength is reduced, the development of the optical scanning device depends on the practical use of the short wavelength laser, and it takes time to reduce the cost of the laser. You. In addition, there are various problems with the use, such as the shortening of the wavelength, the required processing accuracy of optical components becomes stricter, the problem of optimizing the absorption of materials and the characteristics of the photoconductor according to the wavelength. Can be

It is difficult to design the F-number of the scanning optical system brightly, especially in the case of the scanning optical system, because of the restriction of the arrangement from the deflector to the surface to be scanned. . Also, a small change does not provide a sufficient effect.

On the other hand, there is an attempt to make an imaged spot on a scanned surface into a minute spot using an apodization method or the like.
even if the diameter of e ² is smaller, the sidelobe height even higher, which streaks were not practical there are problems such as may appear in the image due.

The present invention provides an optical scanning device suitable for high-definition printing by performing multiple scanning on the same scanning line on a CCD or a photoreceptor surface with an appropriate imaging spot light, and an image forming apparatus using the same. Aim.

[0009]

According to the first aspect of the present invention, an optical scanning device deflects a plurality of light beams by a deflecting device, and sequentially scans substantially the same area on the surface to be scanned with the plurality of deflected light beams. That is, a multi-valued light amount is given to the surface to be scanned.

The optical scanning device according to the second aspect of the present invention deflects a plurality of light beams by a deflecting means, and sequentially optically scans one main scanning line on the surface of the photoreceptor with the plurality of deflected light beams. It is characterized in that a plurality of exposures are given on a scanning line, and a multi-level exposure amount distribution is given to the photoreceptor.

According to a third aspect of the present invention, the first exposure of the plurality of exposures is an exposure of a high-density continuous first pattern in which an exposed portion and an unexposed portion are repeated. The second exposure is characterized in that it is an exposure of a second pattern modulated according to an information signal to be recorded.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the exposure of the second pattern is performed so as to overlap the first pattern, and the second pattern has a cycle of the pattern as compared with the first pattern. Are sparse.

A fifth aspect of the present invention is characterized in that, in the third or fourth aspect of the invention, the first exposure and the second exposure are each performed by binary modulation of a light beam from a light source.

According to a sixth aspect of the present invention, in the second aspect of the present invention, each of the plurality of deflected light beams scans the same scanning line continuously on the surface of the photosensitive member with an image forming spot, and scans the preceding image forming spot. It is characterized in that the subsequent imaging spot scans following.

According to a seventh aspect of the present invention, in the second aspect of the present invention, the first exposure is performed by a preceding imaging spot that scans the same scanning line, and the second exposure is performed by the first exposure. Is performed by using an image forming spot that follows the exposure.

According to an eighth aspect of the present invention, in the third aspect of the present invention, of the plurality of exposures, the first exposure is means for continuously modulating a light source at a high speed in order to provide a high-density continuous pattern exposure on a photosensitive member. It is special that it is used.

According to a ninth aspect of the present invention, in the third aspect of the present invention, the first exposure is a phase shift mask in a light beam for providing a high-density continuous pattern exposure on the photosensitive member. Are arranged, and means for miniaturizing an image forming spot is used.

According to a tenth aspect of the present invention, in the third aspect of the present invention, the first of the plurality of exposures is performed so that a high-density continuous pattern is exposed on the photosensitive member. A prism for distributing the light beam to the peripheral portion is disposed, and means for miniaturizing an image forming spot is used.

According to an eleventh aspect of the present invention, in the second aspect of the present invention, the photoreceptor becomes a developable electrostatic latent image when the exposure amount exceeds a certain threshold value, and does not become an image otherwise. It has a characteristic that, among a plurality of exposures, an exposure amount by only the first exposure and an exposure amount by only the second exposure do not reach a threshold value that can be developed alone.

According to a twelfth aspect of the present invention, in the second aspect of the present invention, the photoreceptor has a γ characteristic such that the exposure amount becomes a developable electrostatic latent image when the exposure amount exceeds a certain threshold, and the image does not become an image when the exposure amount does not exceed the threshold. In a region where both the first exposure and the second exposure have been performed among a plurality of exposures, when the exposure amounts of both are added to exhibit a multi-level exposure amount, It is a special feature that there is a developable threshold below the maximum value of the multi-level exposure.

According to a thirteenth aspect of the present invention, the plurality of light beams are deflected by the deflecting means, and the plurality of deflected light beams are sequentially optically scanned on one main scanning line on the surface of the photoreceptor. A plurality of exposures are given on a scanning line, and a plurality of similar exposures are given to a plurality of rows in the sub-scanning direction, so that a multi-level exposure amount distribution is given to the photoconductor.

According to a fourteenth aspect of the present invention, there is provided an image forming apparatus comprising: the optical scanning device according to any one of the first to thirteenth aspects; and a toner image formed by scanning the photosensitive member with a light beam. And a transfer unit for transferring the developed toner image to a sheet of paper, and a fixing unit for fixing the transferred toner image to the sheet of paper.

[0023]

[First Embodiment] FIG. 1 is a schematic view of a main part of a first embodiment of the present invention. The light source 1 is a two-beam array laser composed of a laser A and a laser B. The two optical beams La and Lb emitted from the laser 1 are used as an incident optical system 2 composed of a collimator lens, a cylinder lens, and the like.
Is introduced into the deflector 3 via
An image is scanned and formed on a photosensitive drum 5 and a CCD through an emission optical system 4 such as a θ lens.

In some cases, the two light beams La and Lb may be formed by splitting light beams from the same laser with a light splitter or the like.

The number of light beams is not limited to two, but may be three or more.

The two light beams La and Lb are configured to scan the same scanning line on the drum at a predetermined distance. One imaging spot La starts scanning on the scanning line first, and then scans on the same scanning line with a slight delay so that the subsequent imaging spot Lb follows it.

The preceding imaging spot La is a high-resolution continuous repetition pattern in the main scanning direction as a first exposure.
Scanning is performed while giving an exposure amount on the photoconductor 5. At this time, the preceding imaging spot La scans while being intensity-modulated at a high speed with a very short time pulse compared to a case where writing is generally performed by one exposure. As a result of this operation, a very short period of shallow exposure is provided along the scan line. FIG. 2 schematically shows an exposure amount given on the photoconductor as a result of the first exposure.

As shown in the figure, when the image forming spot La is driven and exposed by a high-speed continuous pulse, a small exposure amount distribution is formed at a high frequency as shown in the lower figure. T in FIG.
The level indicated by h is a level (threshold) at which an electrostatic latent image is formed only when the exposure amount reaches this level, that is, an image appears after the development process.

The amount of exposure is defined as the product of the magnitude of light energy and the time during which it is irradiated. The photoreceptor used in the present invention has such a characteristic that, when a given exposure amount reaches a predetermined level, an image appears rapidly after the development process, so-called high γ. When the exposure amount exceeds a certain threshold value, the image becomes a developable electrostatic latent image, and when the exposure amount does not exceed the threshold value, the image does not become an image.

In the present embodiment, no image is developed as a toner image after development, even if the development process is performed in a state where only the first exposure has been performed. That is, in the state where only the first exposure is performed, the exposure amount does not reach the developable level th. This is because when a short-period pulse exposure is forcibly performed on an imaging spot having a certain size, the lighting time of the light source has to be shortened, so that the exposure amount is reduced and such exposure is inevitably performed. Easy to be quantity. This is shown in FIG. If the exposure pulse is lengthened so that the exposure amount reaches the developable level th, the exposure pattern becomes large.

In general, when an exposure of a pattern having a high resolution compared to the spot size is to be realized with a sufficient exposure amount, on the contrary, if the exposure amount is to be provided to a developable level. It is necessary to increase the magnitude of the absolute power of the light beam irradiated to the photoreceptor via the scanning lens, or to lengthen the pulse exposure time.

First, it is difficult to increase the amount of light radiated from the light source due to the limitations of the semiconductor laser, and it is not easy to increase the brightness of the optical system due to the limitations of the device configuration. exclude. Next, increasing the lighting time would increase the spatial length of the pattern to be exposed, which would reduce the resolution of the image to be exposed, and inevitably lead to a low exposure state . On the other hand, if it reaches the development level, it is necessary to reduce the amount of light radiated from the light source. As a result, the minimum size (highest frequency) that can be marked with the size of the imaging spot is limited.

In the present embodiment, the first exposure is performed with such a high-resolution and simple continuous pattern, but the exposure amount has not reached the developable level. Next, a second exposure with the emission time controlled based on normal image information is performed in a double overlapping manner from above, thereby creating a multi-level state in the exposure amount irradiated on the photoconductor. ing. The second exposure is, for example, a level of exposure at which no toner image appears, as in the case of the first exposure alone, even if the developing process is performed immediately after the second exposure is performed alone.
Incidentally, the light emission control for the second exposure is not necessarily performed in accordance with the image information itself to be printed, and is adjusted so that the exposure pattern after addition described later becomes a desired image after development. There is also.

The state in which the two exposure amounts are superimposed generally means that the high-definition pattern applied by the first exposure and the print pattern by the second exposure are added. As a result, the exposure amount exhibits a multilevel exposure amount level as shown in FIG. By passing the exposure amount distribution through a process of performing development at an appropriate threshold value th, a desired random print pattern by the second exposure is obtained based on the pattern having a high resolution of the first exposure. At the exposure level that can be developed. This state is also shown in FIG.

FIG. 4 shows the size of the print dot when the present invention is not used.

As shown here, the effect of this embodiment is to obtain a high-resolution output in both the main scanning direction and the sub-scanning direction as compared with a dot of an image formed by a conventional conventional imaging spot. Is possible. This is because the pattern of the first exposure can form a high-resolution pattern not only in the main scanning direction but also in the sub-scanning direction.

As described above, in the present embodiment, by using the additive property of the exposure amount of the electrophotographic photosensitive member, the exposure amount is given to the photosensitive member so as to be multi-valued, and the threshold value at which development is possible is appropriately set. That is, by using a photoreceptor having a high 11r characteristic, a high-definition continuous repetition pattern is used as a first exposure, and a second exposure based on an image signal is performed as a base on the first exposure, so that the exposure amount is reduced. The minimum resolvable pattern that can be developed beyond a predetermined threshold is miniaturized.

Further, by using a multi-beam scanning optical system using a two-beam array laser or the like as a light source, multiple exposures such as scanning the photosensitive member twice are realized.

FIG. 5 is a schematic view of a main part of a second embodiment of the present invention. The light source is composed of two lasers A and B. The two diffused light beams emitted from the two lasers A and B are collimated by collimator lenses 2A and 2B, respectively, are combined using a beam splitter 6, and are slightly separated from each other. It is assumed that two light beams La and Lb form an appropriate angle.

This is introduced into the deflector 3 via an incident optical system constituted by a cylinder lens and the like, and the deflected light beam is transferred onto a CCD or photosensitive drum S via an exit optical system 4 such as an fθ lens. Imaging scan is performed.

The two light beams La and Lb are configured to scan the same scanning line on the drum 5 at a predetermined distance. One of the imaging spots Lb starts scanning on the scanning line first, and then, after a short delay, the subsequent imaging spot Lb.
a scans on the same scan line so that a follows it.

The phase shift mask 7 as shown in FIG. 6 is arranged in the optical path immediately before the beam is synthesized by the beam splitter 6 in the light source portion for the preceding imaging spot Lb. More specifically, a band-shaped phase shift mask 7 parallel to the sub-scanning direction is provided on the pupil of the collimator lens 2B.
, And the pupil is divided into approximately three parts at the center and at both ends.

The phase shift mask 7 is configured to shift the phase of the light beam by π. As a result, the image spot on the surface to be scanned has a diameter DH in the cross section in the main scanning direction smaller than a diameter DV in the sub scanning cross section, and instead, the peak of the side lobe on the side surface corresponding to the main scanning direction. IS is higher than the peak of the side lobe on the side surface corresponding to the sub-scanning section direction. This state is schematically shown in the middle part of FIG. The schematic plan view of the imaging spot shows a shape when the imaging spot is cut at a certain intensity slice level. In this case, the slice is sliced at a level slightly lower than the side lobe having a high intensity in the main scanning direction.

As a result, an image spot is formed in which the three peaks of the side lobes IS and the center peak ID on both sides are arranged in the main scanning direction. Using this imaging spot having three peaks in the main scanning direction, a high-resolution and continuous repetitive pattern in the main scanning direction is used as a first exposure, and scanning is performed while giving an exposure amount on the photoconductor 5 in a pulsed manner. I will do it.

At this time, the pulsed lighting control of the image spot is always performed in synchronization with the interval between the side lobe and the center peak. That is, the central peak is turned off once after the pulse exposure, and then is turned on so as to be exposed to the position when the light is moved to the position immediately before the side lobe.

Similarly, the side lobes on the subsequent side are exposed in such a manner that the center peak is superimposed on the position where the center lobe was exposed first. As a result, the width of the substantial exposure area of the center spot is reduced, and the side lobe having a higher peak is lit in synchronization with the shift of the exposure position of the center peak, whereby the height of the side lobe with the pitch as the side lobe radius is increased. It becomes possible to expose a fine periodic pattern.

Generally, when a phase shift mask is used,
Although the spot diameter at the center becomes smaller, the side lobe becomes higher as a disadvantage, which impairs the effect of high resolution.However, when using the method according to the present invention, the peak light amount of the side lobe is also effective for exposure. It does not become an obstacle to use it.

In general, as compared with a case where writing is performed by a single exposure with a normal image forming spot where no phase operation is performed,
An exposure amount of a periodically repeated pattern having a relatively short period and relatively contrast can be applied along a scanning line. FIG. 7 schematically shows the exposure amount given on the photoconductor as a result of the first exposure.

The amount of exposure is defined as the product of the magnitude of light energy and the time during which it is irradiated. The photoreceptor used in the present invention has such a characteristic that, when a given exposure amount reaches a predetermined level, an image appears rapidly after the development process, so-called high γ. When the exposure amount exceeds a certain threshold value, the image becomes a developable electrostatic latent image, and when the exposure amount does not exceed the threshold value, the image does not become an image.

In the present embodiment, no image is developed as a toner image after development even if the development process is performed in a state where the first exposure is performed. That is, in the state of only the first exposure, the exposure amount does not reach the level at which development is possible. This is because when a short-period pulse exposure is forcibly performed on an imaging spot having a certain size, the lighting time of the light source has to be shortened, so that the exposure amount is reduced and such exposure is inevitably performed. Easy to be quantity.

In general, when an exposure of a pattern having a higher resolution than that of the spot size is to be realized with a sufficient exposure amount, on the contrary, if the exposure amount is to be increased to a developable level. It is necessary to increase the magnitude of the absolute power of the light beam irradiated to the photoreceptor via the scanning lens, or to lengthen the pulse exposure time.

First, it is difficult to increase the amount of light radiated from the light source due to the limitations of the semiconductor laser, and it is not easy to increase the brightness of the optical system due to the limitations of the device configuration. exclude. Next, increasing the lighting time would increase the spatial length of the pattern to be exposed, which would reduce the resolution of the image to be exposed, and inevitably lead to a low exposure state . On the other hand, if the light amount reaches a development level due to a sufficient amount of light, it is necessary to reduce the amount of light emitted from the light source.

In the present embodiment, the first exposure is performed with such a high resolution and simple continuous pattern, but the exposure amount has not reached the developable level. Next, the second exposure, the emission time of which is appropriately controlled based on normal image information, is superimposed on the second exposure. Producing.
The second exposure is, for example, a level of exposure at which no toner image appears, as in the case of the first exposure alone, even if the developing process is performed immediately after the second exposure is performed alone. Incidentally, the light emission control for the second exposure is not necessarily performed in accordance with the image information itself to be printed, and is adjusted so that the exposure pattern after addition described later becomes a desired image after development. There is also.

The state of the exposure amount obtained by adding the two exposures is obtained by performing an additive operation of the high-definition pattern applied by the first exposure and the print pattern by the second exposure. Here, the exposure amount has a multilevel exposure amount level as shown in FIG. By passing through a process of performing development with an appropriate threshold th for this exposure amount distribution,
Based on the pattern having the high resolving power of the first exposure, a desired random print pattern by the second exposure can reach a developable exposure level.

As shown in FIG. 8, after performing two exposures, that is, a first exposure and a second exposure, if the modulation degree of the first exposure is not within an appropriate range with respect to a threshold value th, the exposure is performed. It is difficult to develop correctly. To facilitate this,
It is desirable to make the degree of modulation of the exposure amount of the continuous pattern having a high period given by the first exposure as high as possible. As described above, the frequency of a continuous pattern that can be exposed without difficulty compared to the normal imaging spot size is naturally determined.

In this embodiment, the first exposure at a frequency exceeding the limit is required. First, the exposure is not required to be at a developable level. It tends to impair the degree.

Therefore, as a means for increasing the degree of modulation of the exposure amount, the present embodiment discloses a means for improving the repetition spatial frequency of the exposure pattern using a phase shift mask. This has the effect of improving the degree of modulation of the first exposure by providing exposure by superposing the side lobe and the center peak, and exposing the portion to be exposed as it is and by exposing the portion to be exposed. There is a feature that the problem of high light quantity is not a problem.

The lowermost part of FIG. 8 shows the size of the print dot in a case that is not related to the present invention.

FIG. 9 is a schematic view of a main part of a third embodiment of the present invention. The light source is two laser units. The two diffused light beams emitted from the two lasers A and B are collimated by the collimator lenses 2A and 2B, respectively, are combined using the beam splitter 6, and are slightly different from each other. Two light beams La and Lb forming an angle are assumed.

This is introduced into the deflector 3 via an incident optical system composed of a cylinder lens or the like, and the deflected light beam is transferred onto a CCD or photosensitive drum 5 via an exit optical system 4 such as an fθ lens. Imaging scan is performed.

The two light beams La and Lb are configured to scan on the same scanning line on the drum 5 at a predetermined distance. One of the imaging spots Lb starts scanning on the scanning line first, and then, after a short delay, the subsequent imaging spot Lb.
a scans on the same scan line so that a follows it.

For the preceding imaging spot Lb, the phase shift mask 7 is arranged in the light path of the corresponding light source portion immediately before the beam is combined by the beam splitter 6. More specifically, the mask divides the pupil into two at the pupil portion of the collimator lens 2B at a boundary parallel to the sub-scanning direction. The phase shift mask 7 is configured to shift the phase of the light beam by π. As a result, the imaged spot on the surface to be scanned is divided into two in the main scanning direction from the center as shown in FIG. As a result, two substantially semicircular imaging spots whose intensity falls to zero on a straight line parallel to the sub-scanning direction passing through the center of the original imaging spot are presented.

The two imaging spots arranged in the main scanning direction are:
Each peak has the same height. Using this imaging spot having two peaks in the main scanning direction, a high-resolution continuous repetition pattern in the main scanning direction is used as the first exposure, and scanning is performed while giving an exposure amount on the photoconductor in a pulsed manner. Go on.

At this time, there are two types of pulses for driving the imaging spots to be illuminated: the two spot peaks are exposed as one set, and the pulse is lit while the peaks are synchronized one by one.

In the former case, as shown in FIG. 11, two patterns are exposed by two peaks in one lighting operation, and then shifted by two peaks (that is, one imaging spot). It turns on again at the position,
One pattern is exposed for each peak. In the latter case, as shown in FIG. 12, a pulse is emitted in synchronization with each shift of approximately the image spot radius, and the same spot on the photoreceptor surface is scanned once by both peaks of the image spot (total of 2). Times) A high-density continuous pattern is exposed by performing pulse exposure.

The difference in the pattern to be exposed due to the difference in the pulse driving method is that the former requires a pulse driving frequency of の that of the latter, while the contrast of the continuous inversion pattern (the exposure of the exposed portion and the exposed portion is different). (Corresponding to a difference in the amount). On the other hand, when exposure is performed twice each as in the latter case, it is necessary to drive at a high frequency, but on the other hand, exposure with high contrast can be performed. This state is shown in FIG.
1, and shown at the bottom of FIG.

By performing such exposure, it becomes possible to expose a high-definition periodic pattern having a pitch substantially equal to the image forming spot radius. In general, the exposure amount of a periodic repetition pattern having a relatively high contrast and a relatively high contrast along a scanning line is extremely short in comparison with a case where writing is performed by a single exposure using a normal imaging spot where no phase operation is performed. Can be applied. FIG. 13 schematically shows the exposure amount given on the photoconductor as a result of the first exposure.

The amount of exposure is defined by the product of the magnitude of light energy and the time during which it is irradiated. The characteristics of the photoreceptor used in the present embodiment are such that, after undergoing a development process, an image appears rapidly when a given exposure amount reaches a predetermined level, that is, a characteristic called high γ. When the exposure amount exceeds the threshold value th as shown in FIG. 13, the image becomes a developable electrostatic latent image. When the exposure amount does not exceed the threshold value th, the image does not become an image.

In this embodiment, no image is developed as a toner image after development, even if the development process is performed in the state where the first exposure is performed. That is, in the state of only the first exposure, the exposure amount does not reach the level at which development is possible. This is because when a short-period pulse exposure is forcibly performed on an imaging spot having a certain size, the lighting time of the light source has to be shortened, so that the exposure amount is reduced and such exposure is inevitably performed. Easy to be quantity.

In general, when an exposure of a pattern having a higher resolution than the spot size is to be realized with a sufficient exposure amount, on the contrary, if the exposure amount is to be increased to a developable level. It is necessary to increase the magnitude of the absolute power of the light beam irradiated to the photoreceptor via the scanning lens, or to lengthen the pulse exposure time.

First, it is difficult to increase the amount of radiation from the light source due to the limitations of the semiconductor laser. In addition, since it is not easy to increase the brightness of the optical system due to restrictions on the device configuration, these items are excluded.

Next, increasing the lighting time increases the spatial length of the pattern to be exposed, which in turn reduces the resolving power of the image to be exposed. Easy to be. On the other hand, if the light amount reaches a development level due to a sufficient amount of light, it is necessary to reduce the amount of light emitted from the light source.

In the present embodiment, the first exposure is performed with such a high resolution and simple continuous pattern, but the exposure amount has not reached the developable level. Next, the second exposure, the emission time of which is appropriately controlled based on normal image information, is superimposed on the second exposure. Producing.

The second exposure is performed, for example, even if the developing process is performed immediately after the single exposure is performed.
As in the case of the exposure alone, the exposure amount is such that the toner image does not appear. Incidentally, the light emission control for the second exposure is not necessarily performed in accordance with the image information itself to be printed, and is adjusted so that the exposure pattern after addition described later becomes a desired image after development. There is also.

The state of the exposure amount obtained by adding the two exposures is obtained by performing an additive operation of the high-definition pattern obtained by the first exposure and the print pattern obtained by the second exposure. Here, the exposure amount has a multilevel exposure amount level as shown in FIG. By passing the exposure amount distribution through a process of performing development at an appropriate threshold value th, a pattern having a high resolving power of the first exposure is used as a base, and a desired random pattern by the second exposure is obtained. It is possible to make the print pattern reach a developable exposure level.

As shown in FIG. 13, the first exposure and the second exposure
After performing the two exposures described above, it is difficult to correctly develop the first exposure unless the modulation degree of the first exposure is within an appropriate range with respect to the threshold th. In order to facilitate this, it is desirable to make the degree of modulation of the exposure amount of a continuous pattern having a high period given in the first exposure as high as possible.

As described above, the frequency of a continuous pattern that can be exposed without difficulty compared to the normal imaging spot size is naturally determined. In the present embodiment, the first exposure at a frequency exceeding the limit is required. First, the exposure is not required to be at a developable level. However, the exposure alone impairs the degree of modulation of the exposure. Have a tendency.

Therefore, on the other hand, as means for increasing the degree of modulation of the exposure amount, a means disclosed in the present embodiment is a means for improving the repetition spatial frequency of the exposure pattern by using a phase shift mask. As shown in FIG. 12, by additionally performing exposure by superimposing two peaks, the exposed portion is exposed as it is, and the exposed portion is exposed by overlapping.
There is an effect of improving the modulation degree of the first exposure.

The lowermost part of FIG. 13 shows the size of the print dot in the case where the present invention is not applied.

FIG. 14 is a schematic view of a main part of a fourth embodiment of the present invention. In this case, an irregular prism 8 is arranged on the pupil instead of the pupil phase shift mask in the case of the second embodiment.

This prism divides the light beam in the pupil, which is long in the sub-scanning direction, into two in the main scanning direction, and forms a band-like portion through which the light beam does not pass in the center. With this prism, the light beam can obtain the same image spot as that described in the second embodiment due to the so-called apodization effect in the main scanning direction.

Since the luminous flux in the central portion is distributed to both sides, there is no loss of light amount unlike the case where a light shielding plate is used.
Since the light beam is enlarged in the main scanning direction after passing through the deformed prism, it is necessary to reduce the diameter of the collimator so that the other light beam and the F-number are aligned.

The other structure is the same as that of the second embodiment.

In the present invention, the light scanning is sequentially performed on a single scanning line with a plurality of light beams as described in each of the above embodiments by simultaneously performing a similar method on a plurality of scanning lines in the sub-scanning direction. Is also good. [Image Forming Apparatus] FIG. 15 is a cross-sectional view in a sub-scanning direction showing a configuration example of an electrophotographic printer as an example of an image forming apparatus using the optical scanning apparatus (multi-beam optical scanning apparatus) of the present invention. is there. In the figure, reference numeral 100 denotes an optical scanning device (multi-beam optical scanning device) according to any of the embodiments of the present invention described above. Reference numeral 101 denotes a photosensitive drum (photoreceptor) serving as an electrostatic latent image carrier. Above the photosensitive drum 101, a charging roller 102 for uniformly charging the surface of the photosensitive drum 101 is in contact with the surface.

A light beam (light flux) 103 scanned by the optical scanning device 100 is irradiated on the charged surface of the photosensitive drum 101 downstream of the contact position of the charging roller 102 in the rotation direction A downstream. It has become so.

The light beam 103 is modulated on the basis of image data. By irradiating the light beam 103, an electrostatic latent image is formed on the surface of the photosensitive drum 101. The electrostatic latent image is formed as a toner image by a developing device 107 serving as a developing unit disposed so as to be in contact with the photosensitive drum 101 on the downstream side in the rotation direction of the photosensitive drum 101 from the irradiation position of the beam 103. Developed.

The toner image is transferred onto a paper 112 as a transfer material by a transfer roller 108 as a transfer unit disposed below the photosensitive drum 101 so as to face the photosensitive drum 101. The paper 112 is stored in a paper cassette 109 in front of the photosensitive drum 101 (right side in FIG. 15), but can be fed manually. The sheet 112 in the sheet cassette 109 is sent to the transport section.

The sheet 112 onto which the unfixed toner image has been transferred as described above is further moved to the rear of the photosensitive drum 101 (FIG. 1).
5 is conveyed to a fixing device as a fixing unit (left side). The fixing device includes a fixing roller 113 having a heater (not shown) therein and a pressure roller 114 disposed so as to be in pressure contact with the fixing roller 113, and the paper conveyed from the transfer unit. 112 is the fixing roller 1
The unfixed toner image on the sheet 112 is fixed by heating while applying pressure at a pressure contact portion between the pressure roller 13 and the pressure roller 114. Further, behind the fixing roller 113, the sheet discharging roller 1
16 is provided to discharge the fixed sheet 112 out of the printer.

[0089]

According to the present invention, the present invention provides an optical scanning device suitable for high-definition printing by performing multiple scanning on the same scanning line on the surface of a CCD or a photoreceptor with an appropriate imaging spot light, and using the same. Image forming apparatus can be achieved.

In addition, according to the present invention, high-resolution printing is made possible by superimposing the first exposure and the second exposure using a multi-beam optical system. In addition, the size of the imaging spot must be reduced by a combination of the exposure conditions that have a higher resolution than before, but that random printing is not possible (limited to continuous patterns), and the conventional exposure conditions that are random printing but not high resolution. High-resolution printing is possible. In addition, it is possible to effectively improve the printing resolution by using an optical system that basically follows the conditions of the conventional optical system such as wavelength and brightness.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a main part of a scanning optical system according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a first exposure according to the first embodiment of the present invention.

FIG. 3 is a supplementary explanatory diagram of the first exposure according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram of an operation / effect of the first embodiment of the present invention.

FIG. 5 is a schematic diagram of a main part of a scanning optical system according to a second embodiment of the present invention.

FIG. 6 is an explanatory diagram of a pre-formed spot and a filter according to the second embodiment of the present invention.

FIG. 7 is an explanatory diagram of a first exposure according to the second embodiment of the present invention.

FIG. 8 is an explanatory diagram of an operation / effect of the second embodiment of the present invention.

FIG. 9 is a schematic diagram illustrating a scanning optical system according to a third embodiment of the present invention.

FIG. 10 is an explanatory diagram of a preceding imaging spot and a filter according to a third embodiment of the present invention.

FIG. 11 is an explanatory diagram of a first exposure according to a third embodiment of the present invention.

FIG. 12 is an explanatory view of an overlap exposure of a first exposure according to a third embodiment of the present invention.

FIG. 13 is an explanatory diagram of an operation / effect of the third embodiment of the present invention.

FIG. 14 is an explanatory diagram of a preceding image formation spot and a prism according to the fourth embodiment of the present invention.

FIG. 15 is a schematic diagram of a main part of the image forming apparatus of the present invention.

[Explanation of symbols]

 Reference Signs List 1 light source means 2 collimator lens 3 optical deflector 4 Fθ lens 5 photosensitive surface 6 beam splitter 7 phase shift mask 8 irregular prism 100 optical scanning optical system 101 photosensitive drum 102 charging roller 103 light beam 107 developing device 108 transfer roller 109 paper cassette 110 Paper feed roller 112 Transfer material (paper) 113 Fixing roller 114 Pressure roller 116 Paper discharge roller

Continued on the front page F term (reference) 2C362 AA22 AA34 AA40 BA64 BA67 BA84 CA12 CA13 CB02 CB03 CB07 CB08 CB59 2H045 AA01 BA22 CB24 DA22 DA28 5C072 AA03 BA04 BA16 DA10 DA15 HA02 HA06 HA13 HB04 HB08

Claims (14)

[Claims] 1. A plurality of light beams are deflected by a deflecting means, and the deflected light beams sequentially scan substantially the same area on a surface to be scanned to give a multi-valued light amount to the surface to be scanned. An optical scanning device. 2. A plurality of light beams are deflected by a deflecting means, and the plurality of deflected light beams are sequentially optically scanned on one main scanning line on a photoreceptor surface to give a plurality of exposures on the one scanning line. An optical scanning device, wherein a multi-level exposure amount distribution is given to the photoreceptor. 3. The first exposure of the plurality of exposures is an exposure of a high-density continuous first pattern in which an exposed portion and an unexposed portion are repeated, and the second exposure is an information signal to be recorded. 3. The optical scanning device according to claim 2, wherein the exposure is exposure of a second pattern modulated according to the following. 4. The exposure of the second pattern is performed so as to overlap the first pattern, and the second pattern is formed by exposing the first pattern to the first pattern.
4. The optical scanning device according to claim 3, wherein a period of the pattern is smaller than that of the pattern. 5. The optical scanning device according to claim 3, wherein the first exposure and the second exposure are exposures based on binary modulation of a light beam from a light source. 6. The plurality of deflected light beams continuously scan the same scanning line on the surface of the photoconductor with an imaging spot, and a preceding imaging spot is scanned by a subsequent imaging spot. The optical scanning device according to claim 2, wherein: 7. A first exposure among the plurality of exposures is performed by a preceding imaging spot that scans the same scanning line, and a second exposure is performed by an imaging spot that follows the first exposure. 3. The optical scanning device according to claim 2, wherein: 8. The method of claim 1, wherein the first exposure is performed to provide a high-density continuous pattern exposure on the photosensitive member.
4. The optical scanning device according to claim 3, wherein a means for continuously modulating the light source at a high speed is used. 9. A first exposure of the plurality of exposures is performed by disposing a phase shift mask in a light beam to miniaturize an image spot in order to provide a high-density continuous pattern exposure on the photoconductor. 4. The optical scanning device according to claim 3, wherein the optical scanning device uses a unit that performs the operation. 10. A method according to claim 1, wherein the first exposure includes a prism for distributing a light beam at a central portion of the light beam to a peripheral portion of the light beam in order to provide a high-density continuous pattern exposure on the photoconductor. 4. The optical scanning device according to claim 3, wherein means for disposing and miniaturizing an image forming spot is used. 11. The photoreceptor has a γ characteristic such that when the exposure amount exceeds a certain threshold value, it becomes a developable electrostatic latent image, and when the exposure amount does not exceed the threshold value, the image does not become an image. 3. The optical scanning device according to claim 2, wherein the exposure amount based on only the first exposure and the exposure amount based on only the second exposure do not reach threshold values that can be independently developed. 12. The photoreceptor has a γ characteristic such that when the exposure amount exceeds a certain threshold value, the image becomes a developable electrostatic latent image, and when the exposure amount does not exceed the threshold value, the image does not form an image. In a region where both the first exposure and the second exposure are performed, when the exposure amounts of both are added and the multi-level exposure amount is exhibited, the maximum value of the multi-level exposure amount is calculated. 3. The optical scanning device according to claim 2, wherein there is a threshold at which development is possible at a low position. 13. A plurality of light beams are deflected by a deflecting means, and the plurality of deflected light beams are sequentially optically scanned on one main scanning line on a photoreceptor surface to give a plurality of exposures on the one scanning line. , Giving a plurality of similar exposures to a plurality of rows in the sub-scanning direction,
An optical scanning device, wherein a multi-level exposure amount distribution is given to the photoreceptor. 14. An optical scanning device according to claim 1, further comprising: developing means for developing an electrostatic latent image formed by scanning a light beam on the photoreceptor as a toner image; An image forming apparatus comprising: a transfer unit that transfers a developed toner image to a sheet; and a fixing unit that fixes the transferred toner image to a sheet.