JP2004271763A - Optical scanner and image forming device furnished with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily separate a synchronizing signal while realizing the miniaturization and the cost reduction of an optical scanner. <P>SOLUTION: Laser beams Ly, Lk and Lm, Lc emitted from a plurality of light source units 1y, 1k and 1m, 1c which are composed of two semiconductor lasers and two coupling lenses corresponding to the lasers, respectively, are deflected with a rotational deflector 4 in which polygon mirrors 4a and 4b in which the angular phases are vertically dislocated are composed in a unit, photoreceptor drums 20y, 20k and 20m, 20c are scanned in X-direction or Y-direction, as shown with an arrow in the figure, via respective known optical elements, and the laser beams Ly, Lk and Lm, Lc are received with common synchronized sensors 21a and 22a, respectively, thus an easily separable synchronized signal is obtained. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical scanning device for scanning a plurality of image carriers with a plurality of laser beams emitted from a plurality of light source units, respectively, and an image of a printer, a copier, a facsimile, or the like equipped with the optical scanning device. It relates to a forming apparatus.
[0002]
[Prior art]
In recent years, a plurality of laser beams output from a plurality of light sources are emitted as scanning beams, and the respective scanning beams are respectively formed on a plurality of photoconductors as image carriers to form latent images. 2. Description of the Related Art An image forming apparatus such as a color laser printer has been developed which forms a color image by visualizing the above latent images with developers of different colors and sequentially transferring and superimposing the latent images on one sheet of transfer paper. In such an image forming apparatus, since a plurality of scanning units are required to scan the photosensitive member with the laser beam, the number of components is large and the degree of freedom of component arrangement is small as compared with a monochromatic image forming apparatus. As a result, the size of the entire apparatus tends to increase.
However, recently, a color laser printer has been required to be as small as a monochromatic laser printer and to improve productivity, and a plurality of optical beams that emit a plurality of laser beams output from a plurality of light sources as scanning beams have been required. A tandem type image forming apparatus in which a system is housed in one housing and a plurality of photoconductors are provided in parallel has been put to practical use.
[0003]
FIG. 8 is a perspective view showing a schematic configuration of an optical scanning device used in such a tandem type image forming apparatus.
This optical scanning device is a writing unit of a color laser printer that achieves high speed by writing four stations for each color of yellow (Y), black (BK), magenta (M), and cyan (C) corresponding to tandem image formation. The laser beams Ly, Lk, Lm, and Lc emitted from the four light source units 1y, 1k, 1m, and 1c corresponding to the respective colors are respectively used as cylindrical lenses 2y, 2k, 2m, and 2c. , The laser beams Ly and Lc are directly reflected by the mirrors 3k and 3m, and the laser beams Lk and Lm are reflected by the mirrors 3k and 3m, respectively. Form an image. The rotary deflector 4 includes first and second polygon mirrors 4a and 4b having the same angular phase and fixed coaxially at predetermined intervals.
[0004]
The laser beams Ly and Lc are deflected by the upper polygon mirror 4a, and the laser beams Lk and Lm are deflected by the lower polygon mirror 4b so as to scan a predetermined scanning surface. 1, passing through the second fθ lenses 5a and 5b, being reflected by the first folding mirrors 6y, 6k, 6m and 6c, passing through the toroidal lenses 7y, 7k, 7m and 7c, and passing through the second folding mirrors 8y and 8k. The optical paths are deflected by 8m, 8c and third return mirrors 9y, 9k, 9m, 9c, respectively, to form an image on the surface to be scanned on the photosensitive drums 20y, 20k, 20m, 20c and scan in the main scanning direction. .
Although not shown in FIG. 8, synchronous mirrors are provided at both ends of the scanning area of each of the laser beams Ly and Lk and Lm and Lc, and the laser turned back to these synchronous mirrors is provided. Synchronous sensors 21a and 21b for the two laser beams Ly and Lk, and synchronous sensors 22a and 22b for the remaining two laser beams Lm and Lc are provided at positions where the beams can be received. , 21b, 22a, and 22b constitute a synchronous signal detecting means.
As described above, different laser beams are simultaneously made incident on different reflecting surfaces of the upper and lower polygon mirrors 4a and 4b of the rotary deflector 4 so that each polygon mirror can deflect two laser beams. The configuration of the optical scanning device is simplified by sharing a synchronous sensor for two laser beams.
[0005]
[Problems to be solved by the invention]
However, in such a conventional optical scanning device, since the upper and lower polygon mirrors of the rotary deflector have the same angular phase, synchronous light for two optical paths is simultaneously incident on one synchronous sensor. It has been difficult to obtain independent synchronization signals. Therefore, in the optical scanning device shown in FIG. 8, the signals can be separated by slightly (for example, 4 mm) changing the synchronous image height between the laser beams Ly and Lk and Lm and Lc sharing the same synchronous sensor. I have to.
However, in practice, since the image heights of the respective mirrors slightly vary due to the arrangement accuracy of the folding mirrors, etc., in order to reliably separate the synchronization signals, a sufficient difference in the synchronization image heights must be obtained. In such a case, it is necessary to increase the effective scanning area, which results in an increase in the size of various optical elements such as lenses. The image forming apparatus using such an optical scanning device has a problem that the size of the optical device is increased and the entire device is increased in size and the manufacturing cost is increased.
[0006]
FIG. 9 is a timing chart showing the relationship between the output (V) of the synchronous sensor 21a shared by the laser beams Ly and Lk and the time (t) in the conventional optical scanning device shown in FIG. Is a state in which separation based on the image height difference is completed, that is, a state in which the arrangement accuracy is kept good, but in many cases, the state shown in the following (b) tends to be obtained. (B) shows a state where the image heights of the laser beam Ly and the laser beam Lk are close to each other. In the drawing, Yn and BKn indicate output signals (synchronization signals) of the laser beams Ly and Lk on the n-th line, respectively.
In the case where the separation based on the image height difference is achieved as shown in FIG. 9A, the synchronizing signals Yn, BKn and Yn + 1, BKn + 1 of each color are clearly separated, and a good image can be formed. If the separation based on the image height difference is not sufficient as shown in (b), the synchronization signals Yn and BKn and Yn + 1 and BKn + 1 overlap each other, and synchronization cannot be detected, so that good image formation cannot be performed.
[0007]
Further, in order to further improve the productivity in the image forming apparatus provided with such an optical scanning device, it is required to rotate the rotary deflector at a high speed (for example, about 30,000 rpm). When the rotation is started, the synchronization signals of the respective colors shown in FIG. 9 are output at intervals of several μsec, making synchronization separation more difficult, shortening the life of the motor for driving the polygon mirror, and reducing the noise during operation of the apparatus. There is a problem that it increases.
The present invention has been made in view of the above points, and in an optical scanning device and an image forming apparatus provided with the same, stable separation of a synchronization signal and good image formation associated therewith without increasing the length of an optical element. It is another object of the present invention to further reduce the size and cost while making it possible.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a plurality of light source units, a deflecting unit for deflecting a laser beam emitted by a light emitting element arranged in each of the plurality of light source units in a main scanning direction, and a deflecting unit. And a detecting means for detecting each laser beam deflected by the main scanning line on the main scanning line. In the optical scanning device, the detecting means is shared by the laser beams, and the deflecting means are coaxial and have different angular phases from each other. An object of the present invention is to provide an optical scanning device having a plurality of polygon mirrors.
In the above-described optical scanning device, it is preferable that at least one of the light source units includes a plurality of light emitting elements arranged to scan at a predetermined interval in the main scanning direction.
[0009]
In addition, the above-described optical scanning device is provided, and a plurality of image carriers are scanned with the laser beams to form latent images of images to be output, respectively. An image forming apparatus provided with a developing unit for visualizing an image is also provided.
[0010]
Further, in the above-described image forming apparatus, the plurality of image carriers are a plurality of photosensitive members that form latent images corresponding to different colors by scanning with the respective laser beams, and the respective developing units are The latent image formed on each surface of each of the plurality of photoconductors is a means for visualizing with a developer of a different color, and the image of each color visualized by each developing means is formed into one sheet. A color image can be formed by sequentially superimposing and transferring images on a transfer sheet.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings.
FIG. 1 is a perspective view schematically showing the overall configuration of the optical scanning device, FIG. 2 is a side view schematically showing the same, and FIG. 3 is a diagram for simplifying the diagram to facilitate understanding. FIG. 4 is a perspective view showing a configuration and an optical path of one of the stations (Y station), and FIG. 4 is a cross-sectional view schematically showing a configuration of the light source unit. In these figures, parts corresponding to those in FIG. 8 are denoted by the same reference numerals.
Also in this embodiment, the basic configuration of the optical system is the same as that of the conventional optical system shown in FIG. 8, and therefore, the following description will mainly focus on the parts different from FIG. 8 and the parts omitted in FIG. I will.
[0012]
First, the light source units 1y, 1k, 1m, and 1c (hereinafter collectively referred to as "light source unit 1") in this embodiment are semiconductors that are light emitting elements on the same light source holder 10 as shown in FIG. The first and second light sources 11 and 12 made of laser and the first and second coupling lenses 13 and 14 for coupling the two light sources 11 and 12 are formed by known adjusting means (not shown). 1, a multi-beam light source that is adjusted and fixed so that the second laser beams L1 and L2 have a predetermined opening angle in the main scanning direction.
By using the multi-beam light source having such a configuration as the light source units 1y, 1k, 1m, and 1c for each color, the photosensitive drums 20y, 20k, 20m, and 20c can be scanned at predetermined intervals (for example, 8 mm). Will be possible. By adjusting the positions of the first and second light sources 11 and 12 and the first and second coupling lenses 13 and 14 at the time of producing each light source unit, production can be performed with almost no variation. I can do it. Further, by configuring each light source unit in this manner, the number of rotations of the rotary deflector 4 can be reduced, and the life of the polygon motor can be extended and noise can be reduced.
[0013]
Secondly, the rotary deflector 4 of this embodiment has two upper and lower polygon mirrors 4a and 4b whose angular phases are shifted by a predetermined angle (for example, 30 degrees). Can be increased.
FIG. 5 is an optical path diagram when the upper and lower polygon mirrors 4a and 4b are provided with an angular phase difference. The laser beams L1 and L3 or L2 and L4 incident on the rotary deflector 4 from the light sources that have simultaneously emitted light are upper and lower. The light is reflected by the polygon mirrors 4a and 4b, guided to different image height positions on the scanned surface S as reflected beams L1a and L3a or L2a and L4a, and the image height difference and the angle phase difference between the polygon mirrors 4a and 4b are added. Only the interval between the synchronization signals can be increased, and the possibility of inseparability can be eliminated.
In this case, it is not necessary to strictly manage the difference between the angular phases of the upper and lower polygon mirrors 4a and 4b, and it is sufficient if there is a difference equal to or more than a predetermined angle required for separating the synchronization signal. . Also, the manufacturing method may be such that the upper and lower integrated materials are ground with an upper and lower angle phase difference, and two mirrors may be integrated into one shaft by press fitting or shrink fitting. These can be selected at any time according to the manufacturing cost, required reflection surface accuracy, and the like.
[0014]
Here, the detailed configuration and operation of the embodiment having the light source unit and the rotary deflector as described above will be described with reference to FIG. 3 showing a yellow (Y) station as a representative. The light source unit 1y has the first and second light sources 11 and 12 as described above, and is a multi-beam light source including two semiconductor lasers and two collimating lenses, respectively. The upper and lower polygon mirrors 4a and 4b are arranged with a predetermined angular phase difference (for example, 30 degrees).
The laser beam Ly emitted from the light source unit 1y passes through the cylindrical lens 2y, is bent in the optical path by a plurality of mirrors (not shown), and is elongated in the main scanning direction near the deflecting reflection surface of the polygon mirror 4a in the upper stage of the rotary deflector 4. Form a line image. The laser beam Ly that has reached the polygon mirror 4a is deflected so as to scan a predetermined scanning surface, passes through the upper layer of the first fθ lens 5a formed in two layers, and is turned back by the first turning mirror 6y. Then, the light is returned by the second and third return mirrors 8y and 9y through the toroidal lens 7y, passes through the dustproof glass 15y, forms an image on the surface to be scanned of the photosensitive drum 20y, and is scanned.
[0015]
Synchronous mirrors 16a and 16b are provided between the second folding mirror 8y and the third folding mirror 9y at the leading and trailing ends in the scanning direction X, and are reflected by the leading mirror 16a. The laser beam Ly at the end is formed on the photodiode (not shown) of the synchronization sensor 21a, and the laser beam at the end reflected by the synchronization mirror 16b on the rear end is formed on the photodiode (not shown) of the synchronization sensor 21b. Image. The synchronous sensor 21a is used for synchronizing the scanning lines, and the synchronous sensor 21b is used for measuring the scanning speed, that is, the magnification of the image together with the synchronous sensor 21a.
Note that the configuration shown in FIG. 3 has stations for yellow (Y), magenta (M), cyan (C), and black (BK), and therefore is shown in FIG. 3 in FIG. 1 and FIG. The parts corresponding to the respective optical elements are denoted by the same reference numerals with the suffixes y, m, c, and k, respectively.
[0016]
3, the Y station and the BK station are provided on the side shown in FIG. 3, and the C station and the M station are provided on the opposite side, respectively. Synchronous mirrors 17a and 17b and synchronous sensors 22a and 22b are provided on each side, and the rotary deflector 4 is shared by each station, and the synchronous mirrors 16a and 16b and the synchronous sensors 21a and 21b are shared by both Y and BK stations. The apparatus is simplified by sharing the synchronous mirrors 17a and 17b and the synchronous sensors 22a and 22b between the C and M stations. 1 and 2, the laser beams Ly, Lk, Lm, and Lc reflected by the synchronization mirrors 16a, 16b, 17a, and 17b are guided to the synchronization sensors 21a, 21b, 22a, and 22b, respectively. However, other mirrors are provided as needed.
[0017]
In FIGS. 1 and 3, the laser beam immediately inside the outermost laser beam of each of the photosensitive drums 20y, 20k, 20m, and 20c is a synchronous image height, that is, an effective image range (for example, 297 mm for each color). The laser beam indicated by the imaginary line on the outermost side is actually turned halfway and does not reach the surface to be scanned.
[0018]
FIGS. 6A to 6D are timing charts showing the relationship between the sensor output (V) of two laser beams Ly and Lk sharing the same synchronous sensor and the time (t) in this embodiment. , (A) shows the present embodiment, and (b) to (d) show the case where the polygon mirrors 4a, 4b are supposed to have no angular phase difference. In FIG. 6, Y1n and Y2n are output signals of the n-th line emitted from the first and second light sources of the light source unit 1y, and BK1n and BK2n are output signals of the light source unit 1k sharing the same synchronous sensor 21a. It represents the output signal of the n-th line emitted from the first and second light sources.
Even if the angular phase difference between the polygon mirrors 4a and 4b is not provided, if the component precision and the placement precision of each optical element constituting the optical scanning system are good, the image height is increased as shown in FIG. Separation by difference is possible.
However, when the image heights of the laser beams Ly and Lk are separated and approached, as shown in FIGS. 6C and 6D, the output signals BK1n and Y2n or Y1n and BK1n and Y2n and BK2n respectively become Synchronization cannot be detected due to overlap.
However, even in such a state, if an angular phase difference is provided between the polygon mirrors 4a and 4b as in the present embodiment, as shown in FIG. 6A, the output signals Y1n and Y2n and the output signals BK1n and BK2n are Synchronization detection is extremely easy because the interval is large.
[0019]
Next, an embodiment of an image forming apparatus provided with the above-described optical scanning device will be described with reference to FIG. 7, which schematically shows a schematic configuration thereof.
This image forming apparatus is a laser printer in which two-stage paper cassettes 31a and 31b are inserted into a housing 30. In the housing 30, paper feed rollers 32a and 32b that feed the transfer papers of different sizes loaded in the paper feed cassettes 31a and 31b one by one from the top one, and transport those transfer papers. A transport roller 33, a transport belt 34 for transporting the transfer paper for transferring an image to the transfer paper, a fixing roller 35 for fixing the transferred image, and a discharge for discharging the transferred transfer paper. Rollers 36 are provided to form a transfer paper transport path.
Then, four-color photosensitive drums 20m and 20c as image carriers for forming images of magenta (M), cyan (C), yellow (Y), and black (BK) on the conveyor belt 34 are formed. , 20y, and 20k are arranged along the transfer direction of the transfer paper, and each of the photosensitive drums 20m, 20c, 20y, and 20k is rotated in the direction indicated by the arrow.
[0020]
The above-described optical scanning device is arranged in the direction of each of the photosensitive drums 20m, 20c, 20y, and 20k, and four laser beams Lm, Lc, Ly, and Ly are provided through four window holes provided on the lower surface of the case. Lk is emitted, and the surface of each of the photosensitive drums 20m, 20c, 20y, and 20k charged by a charging charger (not shown) is scanned to form an electrostatic latent image.
A developing device as a developing unit that stores magenta, cyan, yellow, and black developers on the downstream side of the scanning positions of the respective photosensitive drums 20m, 20c, 20y, and 20k by the laser beams Lm, Lc, Ly, and Lk. 37m, 37c, 37y, and 37k are provided, and each developing device is provided with a unit case, a toner cartridge as a developer, and a developing roller.
[0021]
Further, a transfer roller is provided at a position facing each of the photosensitive drums 20m, 20c, 20y, and 20k with the transport belt 34 interposed therebetween, and a cleaning unit is provided at a downstream side of the transfer roller. The illustration is omitted.
The latent images formed by scanning the laser beams Lm, Lc, Ly, and Lk on the surfaces of the photosensitive drums 20m, 20c, 20y, and 20k are respectively magenta and cyan by the developing units 37m, 37c, 37y, and 37k. , Yellow, and black developers to visualize the images, transfer the respective images in a superimposed manner onto transfer paper fed from one of the paper feed cassettes 31a and 31b and transported by the transport belt 34, After being fixed by heating and pressing by the fixing roller 35, the sheet is discharged to the outside by a sheet discharging roller 36.
Needless to say, this optical scanning device can be applied to other image forming apparatuses using an optical scanning device using a laser beam, such as a copying machine other than a laser printer and a facsimile machine. In the above-described optical scanning device, all light source units are multi-beam light sources. However, this is not always necessary, and a plurality of light source units having a single beam light source may be arranged. In this case, since the surfaces of the two polygon mirrors have different phases, the signals can be sufficiently separated by the phase difference. For example, by providing a phase difference, an interval of 1/2 of the maximum scanning width (150 mm for the A3 machine) can be easily provided. Of course, by further adding the image height difference due to synchronization in each beam, each signal can be more clearly separated. Furthermore, a plurality of light source units may be provided by providing this composite form, that is, a light source unit in which a single beam light source is arranged and a light source unit in which a plurality of beam light sources are arranged.
[0022]
【The invention's effect】
As described above, according to the present invention, the following effects can be obtained.
According to the optical scanning device of the present invention, further downsizing and cost reduction can be achieved while enabling stable separation of a synchronization signal and accompanying good image formation without increasing the length of the optical element. At the same time, it is not necessary to rotate the polarizing means at high speed, and it is possible to extend the life and reduce the noise during operation.
According to the image forming apparatus provided with the above-described optical scanning device, by using the above-described optical scanning device as a writing unit of the image forming device, a stable image can be obtained without increasing the size and cost of the device. It is possible to form a color image forming apparatus which is small and inexpensive.
[Brief description of the drawings]
FIG. 1 is a perspective view schematically showing an overall configuration of an optical scanning device according to the present invention.
FIG. 2 is also a schematic side view of the same.
FIG. 3 is a perspective view showing one configuration and an optical path of each station in FIG. 1;
FIG. 4 is a cross-sectional view schematically showing the light source unit.
FIG. 5 is an optical path diagram showing an optical path deflected by the rotating polarizer.
FIG. 6 is a timing chart showing the relationship between the output of the synchronous sensor and time.
FIG. 7 is a configuration diagram schematically showing an embodiment of an image forming apparatus according to the present invention.
FIG. 8 is a perspective view schematically showing a conventional optical scanning device.
FIG. 9 is a timing chart showing the relationship between the output of the synchronous sensor and time.
[Explanation of symbols]
1y, 1k, 1m, 1c: light source units 2y, 2k, 2m, 2c: cylindrical lens 4: rotary deflector 5a: first fθ lens 5b: second fθ lens 6y, 6k, 6m, 6c: first Return mirrors 7y, 7k, 7m, 7c: Toroidal lenses 8y, 8k, 8m, 8c: Second return mirrors 9y, 9k, 9m, 9c: Third return mirror 10: Light source holder 11: First light source 12: Second light source 13, 14: coupling lens 16a, 16b, 17a, 17b: synchronous mirror 20y, 20k, 20m, 20c: photosensitive drum 21a, 21b, 22a, 22b: synchronous sensor 30: housing 31a, 31b: Paper feed cassettes 32a, 32b: paper feed roller 33: transport roller 34: transport belt 35: fixing roller 36: paper discharge rollers 37y, 37k, 37 m, 37c: developing unit Lm: laser beam for magenta Lc: laser beam for cyan Ly: laser beam for yellow Lk: laser beam for black

Claims (4)

A plurality of light source units, a deflecting means for deflecting the laser beams emitted by the light emitting elements arranged in the plurality of light source units in the main scanning direction, and deflecting the laser beams deflected by the deflecting means on a main scanning line. An optical scanning device comprising:
The optical scanning device according to claim 1, wherein the detecting means is shared by the laser beams, and the deflecting means has a plurality of polygon mirrors having different angular phases synchronously. 2. The optical scanning device according to claim 1, wherein at least one of the light source units includes a plurality of light emitting elements arranged so as to scan at predetermined intervals in the main scanning direction. . The optical scanning device according to claim 1 or 2, wherein a plurality of image carriers are scanned with the respective laser beams to form latent images of images to be output, respectively, and the image carrier is provided for each of the image carriers. An image forming apparatus comprising a developing unit for visualizing a latent image. 4. The image forming apparatus according to claim 3, wherein the plurality of image carriers are a plurality of photoconductors that form latent images corresponding to different colors by scanning with the respective laser beams, and each of the developing units is Means for visualizing the latent image formed on each surface of each of the plurality of photoreceptors with a developer of a different color. An image forming apparatus characterized in that a color image is formed by sequentially superimposing and transferring images on a transfer sheet.

Images