JP4412906B2 - Optical scanning device and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine thereof. In particular, the present invention relates to an electrophotographic image forming apparatus in which an electrophotographic process is repeated to sequentially form images on an image carrier, the images are sequentially transferred, and the images are recorded on a recording medium such as paper or an OHP film. The present invention also relates to an optical scanning apparatus that performs optical scanning to form an image and writes on an image carrier in such an image forming apparatus.
[0002]
[Prior art]
In an optical scanning device provided in a copying machine, an optical scanning path is formed by providing optical components such as a light source, a polygon mirror, various lenses, and a reflection mirror in an optical housing, and for example, laser light from the light source is reflected by the polygon mirror. Then, the deflection scanning is performed, and the deflected light beam passes through the scanning lens, is reflected by the mirror, is emitted to the outside of the optical housing, and the emitted light is irradiated to perform writing on the image carrier.
[0003]
In such an optical scanning device, the pixel density in the main scanning direction is determined by the writing clock frequency and the main scanning speed by the lens optical system. Keeping the writing density accurate is important for obtaining good image quality. In addition, in an optical scanning apparatus having a plurality of optical scanning paths such as a color image forming apparatus, when the pixel density is different in each optical scanning path, images written using the respective optical scanning paths are superimposed. Color misregistration will occur. Therefore, it is particularly important to keep the writing density accurate.
[0004]
For this reason, in a conventional optical scanning device, a pair of photodetectors are arranged on the writing position side and writing end position side outside the image area of the optical scanning path, and main scanning between two points is performed according to their detection timing. There is one in which time is measured, a fluctuation amount from a target main scanning magnification is calculated from the measurement result, and a writing clock frequency is changed from the fluctuation amount to correct a main scanning magnification error.
[0005]
However, in this type of optical scanning device, since the pair of photodetectors are directly mounted on the optical housing, the distance between the pair of photodetectors changes due to thermal deformation of the optical housing due to ambient temperature changes. Therefore, an accurate scanning time could not be obtained.
[0006]
[Patent Document 1]
In the conventional optical scanning device, for example, as described in Patent Document 1, a pair of photodetectors are arranged on the optical scanning path from the writing position to the writing end position. There is an optical scanning apparatus that measures the scanning time of at least one of the pair of photodetectors attached to an optical housing via an intermediate member having a larger thermal expansion coefficient.
[0007]
Then, the amount of thermal deformation of the optical housing and the amount of thermal deformation of the intermediate member are offset to reduce the variation in the distance between the pair of photodetectors due to the influence of heat.
[0008]
[Problems to be solved by the invention]
However, as a practical matter, it has never been easy to offset the amount of thermal deformation of the optical housing and the amount of thermal deformation of the intermediate member. Further, in an optical scanning apparatus having a plurality of optical scanning paths, the optical housing and the intermediate member of each optical scanning path do not always cause the same thermal deformation, and the difference between the thermal deformation amounts between the optical scanning paths. In the case of a color image forming apparatus, there is a problem that color misregistration occurs.
[0009]
SUMMARY OF THE INVENTION Accordingly, a first object of the present invention is to provide an optical scanning device that is easy to manufacture, less affected by thermal deformation, reduces the variation in the distance between a pair of photodetectors used in one optical scanning path, and performs scanning. It is to enable accurate measurement of time.
[0010]
A second object of the present invention is to reduce the positional fluctuation of each photodetector by reducing the influence of thermal deformation in the optical scanning device.
[0011]
A third object of the present invention is to reduce the writing position deviation when writing is started by reducing the influence of thermal deformation.
[0012]
A fourth object of the present invention is to reduce positional deviation between a plurality of optical scanning paths.
[0013]
A fifth object of the present invention is to further reduce the positional deviation between a plurality of optical scanning paths.
[0014]
A sixth object of the present invention is to obtain an image forming apparatus including an optical scanning device that achieves the above-described object.
[0015]
The seventh object of the present invention is to make the influence of the thermal deformation of the optical housing completely negligible and to reduce the position fluctuation of each photodetector.
[0016]
[Means for Solving the Problems]
Therefore, the invention described in claim 1 is to achieve the above first and third objects.
In an optical scanning device comprising an optical component in an optical housing to form an optical scanning path, and a pair of photodetectors arranged in the optical scanning path to measure a scanning time from a writing position to a writing end position,
A pair of photodetectors is attached to the optical housing via an intermediate member having a smaller coefficient of thermal expansion,
The intermediate member is formed in a straight line when the optical scanning device is viewed in plan, and only the writing position side of the intermediate member is fixed to the main body frame on the image forming apparatus side together with the optical housing. It is characterized by that.
[0017]
According to a second aspect of the present invention, in order to achieve the second object described above, in the optical scanning device according to the first aspect, an intermediate member is attached to a portion where the thermal deformation of the optical housing is the smallest. To do.
[0019]
The invention described in claim 3 is characterized in that a plurality of optical scanning paths are formed in the optical scanning device described in claim 1 in order to achieve the fourth object described above.
[0020]
According to a fourth aspect of the present invention, in order to achieve the fifth object described above, in the optical scanning device according to the third aspect , the thermal expansion coefficients of the intermediate members provided in the respective optical scanning paths to be formed are made different. It is characterized by that.
[0021]
According to a fifth aspect of the present invention, there is provided an image forming apparatus including the optical scanning device according to any one of the first to fourth aspects, in order to achieve the sixth object described above.
[0022]
According to a sixth aspect of the present invention, in order to achieve the seventh object described above, in the image forming apparatus according to the fifth aspect, the optical housing is simultaneously formed by using the mounting member for attaching the intermediate member to the optical housing. It is fixed to the main body frame on the apparatus main body side.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an overall schematic configuration of an internal mechanism of a two-color black and red laser copying machine (image forming apparatus) provided with an optical scanning device according to the present invention.
[0024]
Reference numeral 10 in the drawing denotes a copying machine main body. The apparatus main body 10 is placed on the medium storage table 31. An automatic document feeder (ADF) 28 is mounted on the apparatus main body 10 so as to be freely opened and closed.
[0025]
In the copying machine main body 10, a drum-shaped photosensitive member 11 as an image carrier is provided, and a first charging device 12, a first developing device 13, a second charging device 37, a second writing device 38, and the like are disposed around the photosensitive drum 11. A second developing device 39, a transfer / conveyance device 14, a cleaning device 15 and the like are arranged.
[0026]
Above them, a first writing device 16 which is an optical scanning device according to the present invention is provided. The first writing device 16 includes optical components such as a light source (not shown), an optical system 40, a polygon scanner unit having a polygon mirror 41 and a polygon motor 42, a scanning optical system 43, and a mirror 44 in an optical housing.
[0027]
The photoconductor 11 and the devices 12 to 16 and 37 to 39 constitute an image forming device A.
[0028]
A fixing device 17 is provided in parallel with the photosensitive member 11 on the left side of the cleaning device 15 of the image forming apparatus A in the drawing. The fixing device 17 is provided with a fixing roller 18 incorporating a heater as a heat source, and a pressure roller 19 that presses against the fixing roller 18 from below.
[0029]
A document reading device 20 is provided in the upper part of the apparatus main body 10. The document reading device 20 is provided with a light source a, a plurality of mirrors b, an imaging lens c, an image sensor d such as a CCD, and the like.
[0030]
On the other hand, a double-sided unit 22 and a medium cassette 23 are provided in two upper and lower stages in the lower part of the apparatus main body 10. Each of the duplex unit 22 and the medium cassette 23 is provided with a conveyance path that leads to a supply path 24 that extends to a transfer position B below the photoreceptor 11. The duplex unit 22 is branched from the middle of the discharge path 25 extending from the outlet of the fixing device 17 to form a reverse path 26.
[0031]
By the way, a manual feed tray 29 for guiding a manual recording medium to the supply path 24 is provided on the right side surface of the apparatus main body 10 shown in FIG. On the other hand, a stack tray 30 that receives a recording medium discharged through the discharge path 25 is provided on the left side surface of the apparatus main body 10.
[0032]
A contact glass 27 is installed on the upper surface of the apparatus main body 10. An automatic document feeder 28 is mounted on the apparatus main body 10 so as to cover the contact glass 27.
[0033]
The automatic document feeder 28 includes a document table e on which a document is placed, a discharge table f on which a read document is placed, a document conveyance path g extending from the document table e to the discharge table f, and a document table e. A document feeding roller h for feeding out the document and a plurality of document transport rollers i for transporting the document on the document transport path g.
[0034]
By the way, medium cassettes 23 similar to those described above are provided in multiple stages in the medium storage table 31 on which the apparatus main body 10 is placed.
[0035]
Incidentally, when making a copy using the laser copying machine shown in FIG. 1, a main switch (not shown) is turned on and a document is set on the document table e of the automatic document feeder 28. Alternatively, the automatic document feeder 28 is opened and a document is set directly on the contact glass 27, and then the automatic document feeder 28 is closed to press the document.
[0036]
When the start switch is pressed, when a document is set on the automatic document feeder 28, the document set on the document table e shown in FIG. 1 is put into the document transport path g by the document feed roller h and the document transport roller. After being conveyed by i and moved onto the contact glass 27, the document reading device 20 is driven to read the contents of the document by color and discharge it onto the discharge table f. On the other hand, when a document is set on the contact glass 27 in advance, the document reading device 20 is immediately driven, and the document is read by the document reading device 20 by color. The contents of the original read in such a manner are converted into black and red electrical digital image signals.
[0037]
At the same time, in the image forming apparatus A, the photosensitive member 11 is rotated clockwise in the drawing, and the surface is first uniformly charged by the first charging device 12, and then read by the document reading device 20 described above. In accordance with the read contents, the laser beam L is irradiated on the basis of the black digital image signal and black writing is performed by the first writing device 16 to form an electrostatic latent image on the surface of the photoconductor 11, and then the first A black toner image is formed by attaching black toner to the developing device 13 and visualizing the electrostatic latent image.
[0038]
Subsequently, it is uniformly charged by the second charging device 37, and then the laser beam is irradiated by the second writing device 38 based on the red digital image signal in accordance with the reading content read by the document reading device 20 described above. In this way, red writing is performed, and an electrostatic latent image corresponding to the red component of the color original is formed on the black toner image, and then the second developing device 39 attaches red toner to the electrostatic latent image. A red toner image in which the latent image is visualized is formed. As a result, a two-color toner image composed of a black toner image and a red toner image is formed on the photoreceptor 11.
[0039]
At the same time when the start switch is pressed, a medium cassette 23 loaded with recording media such as paper and OHP film is selected from a plurality of medium cassettes 23 provided in multiple stages in the apparatus main body 10 and the medium storage table 31 as appropriate. Then, the recording medium is fed out by rotating the feed roller 33 of the medium cassette 23, put into the supply path 24, transported by the transport roller 34, and abutted against the registration roller 35 and stopped. Then, the registration roller 35 is rotated in synchronism with the rotation of the photoconductor 11, and is sent below the photoconductor 11.
[0040]
Alternatively, the feeding roller 36 in the manual feed section is rotated to put a manual recording medium set on the open manual feed tray 29 into the supply path 24, which is similarly abutted and stopped by the registration roller 35, and then the photoconductor 11. Is sent to the lower side of the photosensitive member 11 in synchronization with the rotation of the photosensitive member 11.
[0041]
Then, as described above, the two-color toner images are transferred to the recording medium fed below the photoreceptor 11 at the transfer position B of the transfer / conveyance device 14 to form a transfer image. After the transfer image is formed, the photoconductor 11 is cleaned with a cleaning device 15 to remove residual toner and prepare for the next similar image formation.
[0042]
On the other hand, the recording medium after the transfer image is formed is conveyed by the transfer / conveyance device 14 and placed in the fixing device 17, and heat and pressure are applied by the fixing roller 18 and the pressure roller 19 to fix the transferred image. Thereafter, the sheet is discharged to the discharge tray 30 through the discharge path 25.
[0043]
When recording images on both sides of the recording medium, they are put from the discharge path 25 into the reversing path 26, reversed by the duplex unit 22, and again into the supply path 24, and separately formed on the photoreceptor 11 on the back surface of the recording medium. After the toner image is transferred to form a transfer image, the transfer image is fixed by the fixing device 17 and discharged to the discharge tray 30.
[0044]
FIG. 2 shows a schematic configuration of the first writing device 16 which is an optical scanning device according to the present invention.
[0045]
Reference numeral 50 in the figure denotes a main body frame (part on the image forming apparatus main body side) provided in the copying machine main body 10. The optical housing 51 is screwed to the main body frame 50 at the position p. In the optical housing 51, for example, mounted on a resin base member 51a, as described above, the light source 45, the optical system 40, the polygon mirror 41 having a mirror on the side of the regular polygon, and the polygon motor 42 for rotating the polygon mirror 41 at high speed. Are provided with optical components such as a polygon scanner unit 46, a scanning optical system 43, and a mirror 44, which form an optical scanning path.
[0046]
Laser light from a light source 45 such as a laser diode is shaped by an optical system 40 including a collimating lens and an aperture, guided to a polygon scanner unit 46, reflected by a polygon mirror 41 rotated by a polygon motor 42, and deflected and scanned. Then, the fθ lens 47 constituting the scanning optical system 43 changes the equiangular scanning by the polygon mirror 41 to the constant-velocity linear scanning, and the surface tilting correction lens (BTL) 48 constituting the scanning optical system 43 also causes the face tilt of the polygon mirror 41. After correcting such errors, the light is reflected by the mirror 44 and guided to the photoreceptor 11.
[0047]
By the way, in the illustrated first writing device 16, mirrors 53 and 54 are provided outside the effective exposure area of the scanning light from the polygon scanner unit 46, and the scanning light is reflected and guided to the photodetectors 55 and 56, respectively. The pair of photodetectors 55 and 56 are attached on the base member 51 a of the optical housing 51 via the intermediate member 57. Then, they are arranged at the writing position and writing end position outside the image area on the optical scanning path, and the scanning time from the writing position to the writing end position is measured by detecting the laser light guided by the mirrors 53 and 54.
[0048]
The intermediate member 57 has a small thermal expansion coefficient than the base member 51a of the optical housing 51, in the position p of the optical housing 51 as described above, the mounting screws for fixing to the main body frame 50 is a part of the copying machine main unit 10 side At the same time, the writing position side is fastened together with the optical housing 51 using the mounting member.
[0049]
In this way, the influence of the thermal deformation of the optical housing 51 can be completely ignored, and the position fluctuations of the photodetectors 55 and 56 can be reduced. Further, by attaching the writing position side of the intermediate member 57 to the optical housing 51, it is possible to reduce the influence of the thermal deformation and to reduce the writing position shift when starting writing.
[0050]
If the intermediate member 57 cannot be attached to the attachment portion of the optical housing 51 fixed to the main body frame 50, the intermediate member 57 is attached so that the writing position side is attached to the portion where the base member 51a has the smallest thermal deformation. Good. In this way, it is possible to reduce the influence of thermal deformation and to reduce the position fluctuation of each of the photodetectors 55 and 56.
[0051]
First, the scanning light is detected by the light detector 55 on the writing position side, then the scanning light is detected by the light detector 56 on the writing end position side, and the scanning time for scanning one line is measured from the detection result. The fluctuation amount from the target main scanning magnification is calculated from the measurement result, and the writing clock frequency is changed from the calculation result to correct the main scanning magnification error.
[0052]
FIG. 3 shows an optical scanning apparatus that has another optical scanning path Lb in addition to the same optical scanning path La as described above, and forms two optical scanning paths.
[0053]
Similarly, another optical scanning path Lb is formed by the laser light from the light source 45A, such as a laser diode, shaped by the optical system 40A, guided to the polygon scanner unit 46, and reflected by the polygon mirror 41 rotated by the polygon motor 42. Deflection scanning is performed, the equi-angle scanning by the polygon mirror 41 is changed to the constant-velocity linear scanning by the fθ lens 47A constituting the scanning optical system 43A, and the polygon mirror 41 is made by the surface tilt correction lens (BTL) 48A which also constitutes the scanning optical system 43A. After correcting errors such as surface tilt, the light is reflected by the mirror 44A and guided to the photoconductor 11.
[0054]
Then, mirrors 53A and 54A are provided outside the effective exposure area of the scanning light from the polygon scanner unit 46, and the scanning light is reflected and guided to the photodetectors 55A and 56A, respectively. The pair of photodetectors 55A and 56A is attached on the base member 51a of the optical housing 51 via the intermediate member 57A.
[0055]
In the two optical scanning paths La and Lb, the thermal expansion coefficients of the intermediate members 57 and 57A are made different according to the heat distribution of the optical housing 51, respectively. For example, when the thermal deformation is greater at the installation position of the intermediate member 57A than at the installation position of the intermediate member 57 due to the relationship between the heat source positions of the image forming apparatus main body, the thermal expansion coefficient of the intermediate member 57A is made smaller than that of the intermediate member 57. .
[0056]
In this way, even when the thermal deformation is not uniform in the portion of the optical housing 51, the thermal expansion coefficients of the intermediate members 57 and 57A are adjusted to be different from each other, and the optical scanning paths La and Lb are adjusted. In the case of a color image forming apparatus, color misregistration can be prevented.
[0057]
【The invention's effect】
As described above, according to the first aspect of the present invention, since the pair of photodetectors is attached to the optical housing via the intermediate member having a smaller thermal expansion coefficient, the fabrication is simple and one optical scanning is performed. Compared to the case where a pair of optical detectors used in the path is directly attached to an optical housing with a large coefficient of thermal expansion, the effect of thermal deformation is reduced and their distance fluctuations are reduced, enabling accurate measurement of the scanning time. Misalignment can be eliminated.
[0058]
According to the second aspect of the present invention, in addition to the effect of the first aspect of the invention, the intermediate member is attached to a portion where the thermal deformation of the optical housing is the smallest. The position fluctuation of the detector can be reduced.
[0059]
According to the invention described in claim 1, in addition to the effect of the invention according to claim 1 described above, since the attachment of the writing start position side of the intermediate member to the optical housing, when starting the write with less influence of thermal deformation Can be reduced.
[0060]
According to the invention described in claim 3 , in addition to the effect of the invention described in claim 1 described above, a plurality of optical scanning paths are formed. For example, in an image forming apparatus having a color-specific light scanning path, color misregistration can be eliminated.
[0061]
According to the invention described in claim 4 , in addition to the effect of the invention described in claim 3 , the thermal expansion coefficient of the intermediate member provided in each of the optical scanning paths to be formed is made different. Even when the thermal deformation is not uniform, the positional deviation between the optical scanning paths can be further reduced by changing the thermal expansion coefficient of the intermediate member accordingly.
[0062]
According to the fifth aspect of the present invention, since the image forming apparatus includes the optical scanning device according to any one of the first to fourth aspects, the image can achieve each of the above effects. A forming apparatus can be provided.
[0063]
According to the invention described in claim 6, in addition to the effect of the invention described in claim 5, the optical housing is simultaneously fixed to the main body frame on the image forming apparatus main body side by using the mounting member for attaching the intermediate member to the optical housing. Therefore, the influence of the thermal deformation of the optical housing can be completely ignored, and the position variation of each photodetector can be reduced.
[Brief description of the drawings]
FIG. 1 is a black and red two-color laser copying machine equipped with an optical scanning device according to the present invention, and is an overall schematic configuration diagram of its internal mechanism.
FIG. 2 is a schematic plan view of a first writing device as the optical scanning device.
FIG. 3 is a schematic plan view of an optical scanning device that forms a plurality of optical scanning paths.
[Explanation of symbols]
16 First writing device (optical scanning device)
50 Main body frame (components on the image forming apparatus main body side)
51 Optical housings 55 and 55A Optical detectors 56 and 56A on the writing side Optical detectors 57 and 57A on the writing end position side Intermediate members La and Lb Optical scanning path

Claims (6)

In an optical scanning device comprising an optical component in an optical housing to form an optical scanning path, and a pair of photodetectors arranged in the optical scanning path to measure a scanning time from a writing position to a writing end position,
The pair of photodetectors is attached to the optical housing via an intermediate member having a smaller coefficient of thermal expansion,
While the intermediate member is formed in a straight line when the optical scanning device is viewed in plan, only the writing position side of the intermediate member is fixed to the main body frame on the image forming apparatus side together with the optical housing. An optical scanning device characterized by having a configuration.   The optical scanning device according to claim 1, wherein the intermediate member is attached to a portion where the thermal deformation of the optical housing is the smallest.   The optical scanning device according to claim 1, wherein a plurality of the optical scanning paths are formed.   4. The optical scanning device according to claim 3, wherein the thermal expansion coefficient of the intermediate member provided in each of the plurality of optical scanning paths formed is made different.   An image forming apparatus comprising the optical scanning device according to claim 1. The image forming apparatus according to claim 5 , wherein the optical housing is simultaneously fixed to the main body frame on the main body of the image forming apparatus using an attachment member that attaches the intermediate member to the optical housing.

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