JP4430143B2 - Optical device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light beam that can be used in a laser printer apparatus, a digital copying apparatus, or the like, which is an image forming apparatus that forms an electrostatic image using a light beam and develops the electrostatic image to obtain a visible image. The present invention relates to an optical device that performs exposure scanning.
[0002]
[Prior art]
For example, a light beam can be used for laser printers and digital copying machines, which are image forming devices that form an electrostatic image with a light beam and develop the electrostatic image to obtain a visible image. The optical device includes a semiconductor laser element that emits a light beam corresponding to image data, a first lens group that narrows the cross-sectional beam diameter of the light beam emitted from the semiconductor laser element to a predetermined size and shape, A deflection device that continuously reflects and deflects a light beam narrowed down to a predetermined size and shape by a lens group in a direction perpendicular to a direction in which a recording medium holding a visible image is conveyed, and deflects by the deflection device A second lens group for forming an image of the light beam on a predetermined position of the recording medium.
[0003]
In the optical device described above, the first lens group includes, for example, a collimating lens positioned in the vicinity of the semiconductor laser element, a cylindrical lens that gives a predetermined cross-sectional beam diameter and shape to a parallel light beam that has passed through the collimating lens, and the like. Become.
[0004]
Further, the second lens group provides a different convergence with respect to the deflection angle with respect to the light beam continuously reflected in a predetermined direction by the deflecting device, and is defined by the continuous reflection. It includes two lenses that set the beam diameter at the imaging position to an optimum size in a direction orthogonal to the direction.
[0005]
In addition, since the lens of the same material is used for the first lens group and the second lens group, all the lenses used for the first lens group are made of glass and used for the second lens group. When the lens material is plastic, for example, PMMA, when the temperature changes between 0 ° C. and 50 ° C., the refractive index n changes from 1.4876 to 1.4789, whereby the second lens group. Compared with an optical device in which the imaging position where the light beam that has passed through the beam is actually condensed varies by about ± 12 mm, the variation in the imaging position that occurs with the variation in the refractive index n due to the change in temperature, A lens that can be suppressed to about ± 0.5 mm is incorporated.
[0006]
[Problems to be solved by the invention]
By the way, in the optical device described above, in order to reduce vibration or noise generated by the deflecting device and reduce the cost required for the motor and the polygon mirror constituting the deflecting device, the diameter of the polygon mirror and each reflection of the polygon mirror are reduced. A method of reducing (shortening) the size (length) of the surface has been proposed.
[0007]
However, by reducing (shortening) the size (length) of each reflecting surface of the polygon mirror, the light beam reflected at or near the connecting portion of each reflecting surface also contributes to image formation. There is a problem that the cross-sectional beam diameter of the light beam when the photosensitive drum in the image forming unit is irradiated fluctuates.
[0008]
In addition, as described above, in order to incorporate lenses of the same material into the first lens group and the second lens group, in many cases, a compound lens in which a plastic lens and a glass lens are combined with a cylindrical lens is used. For example, when a method of integrally molding a plastic lens on a lens surface of a glass lens is used, there is a problem that a molding error of the plastic lens is large and uniform optical characteristics cannot be obtained.
[0009]
An object of the present invention is to provide an optical image that can be used in a laser printer apparatus and a digital copying apparatus that are image forming apparatuses that form an electrostatic image using a light beam and develop the electrostatic image to obtain a visible image. In an optical apparatus that performs exposure scanning of a beam, the diameter of the polygon mirror of the deflecting apparatus that deflects and scans the light beam and the size (length) of each reflecting surface of the polygon mirror can be reduced (shortened), and the shape error of the lens surface can be reduced. An object of the present invention is to provide an optical device having a wide management width and capable of reducing the lens cost.
[0010]
[Means for Solving the Problems]
The present invention has been made on the basis of the above-described problems. A first optical member that gives a predetermined optical characteristic to a light beam emitted from a light source, and the predetermined optical characteristic is provided by the first optical member. Given light beam The second A second optical member focused in one direction; With the axis of rotation along the first direction as the center of rotation It has a reflective surface that can be rotated, and this reflective surface In a second direction orthogonal to the first direction A scanning means for scanning the light beam by rotating; an imaging means for forming an image on a scanning object by passing the light beam scanned by the scanning means; and the scanning means. In the second direction And a photodetector that detects the light beam in order to identify the position of the scanned light beam, wherein the first optical member has a first direction and a first direction. Second A first lens having substantially the same power in each of the two directions, wherein the second optical member is a lens in which a glass cylindrical lens and a plastic cylindrical lens are integrated, and passes through the first lens. First of the light beam In the direction A second lens that only gives convergence, In a state viewed from a third direction orthogonal to each of the first direction and the second direction Predetermined shape Become A direction in which a light beam that has an aperture and passes through the first lens is given convergence by the second lens between the first and second lenses The second direction is Orthogonal to First Asymmetric with respect to direction In addition, on the side where the distance from the scanning start end when the light beam is scanned by the scanning means is large, the amount of passing light is large. And a light amount setting member for setting the light intensity of the light beam toward the second lens to an arbitrary ratio, While allowing the light beam from the first optical member to pass through the second lens approximately in the vicinity of the center in the second direction. The beam diameter of the light beam is controlled so that the beam diameter at the reflecting surface of the scanning unit is smaller than the reflecting surface with respect to the light beam emitted from the second optical member, and the light detector includes: The scanning means is provided so as to detect a light beam in an area other than an image area where an electrostatic latent image is formed on a scanning object by being reflected by a connection point of the reflecting surface of the scanning unit and an adjacent reflecting surface. It is an object of the present invention to provide an optical device characterized by detecting a light beam reflected by a connecting point of a reflecting surface of a means and an adjacent reflecting surface.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a digital copying machine as an image forming apparatus having an optical device according to an embodiment of the present invention.
[0012]
As shown in FIG. 1, the digital copying apparatus 1 includes, for example, 10 as an image reading unit and a printer unit 20 as an image forming unit.
The scanner unit 10 has predetermined imaging characteristics for light from the first carriage 11 formed to be movable in the direction of the arrow, the second carriage 12 that is moved by following the first carriage 11, and the light from the second carriage 12. An optical lens 13 to be applied, a photoelectric conversion element 14 that photoelectrically converts light given predetermined imaging characteristics by the optical lens 13 and outputs an electric signal, a document table 15 that holds the document D, and a document D on the document table 15 A document fixing cover 16 to be pressed is provided.
[0013]
The first carriage 11 is provided with a light source 17 that illuminates the document D, and a mirror 18 a that reflects the reflected light reflected from the document D by the light emitted from the light source 17 toward the second carriage 12. Yes.
[0014]
The second carriage 12 has a mirror 18b for bending the light transmitted from the mirror 18a of the first carriage 11 by 90 °, and a mirror 18c for further bending the light bent by the mirror 18b by 90 °.
[0015]
The document D placed on the document table 15 is illuminated by the light source 17 and reflects reflected light in which the brightness of light corresponding to the presence or absence of an image is distributed. The reflected light of the document D enters the optical lens 13 via the mirrors 18a, 18b and 18c as image information of the document D.
[0016]
The reflected light from the document D guided by the optical lens 13 is condensed on the light receiving surface of the photoelectric conversion element (CCD sensor) 14 by the optical lens 13.
Hereinafter, when the start of image formation is input from an operation panel (not shown) or an external device, the first carriage 11 and the second carriage 12 are in a predetermined positional relationship with respect to the document table 15 by driving a carriage drive motor (not shown). After being moved to the home position determined to be, it is moved along the document table 15 at a predetermined speed, so that the image information of the document D, that is, the image light reflected from the document D is reflected by the mirror 18a. The mirror is cut out with a predetermined width along the extending direction, i.e., the main scanning direction, reflected toward the mirror 18b, and the mirror perpendicular to the extending direction of the mirror 18a, i.e., the sub-scanning direction. The image data is sequentially taken out in units of the width cut out by 18a, and all image information of the document D is guided to the CCD sensor 14. The electrical signal output from the CCD sensor 14 is an analog signal, converted into a digital signal by an A / D converter (not shown), and temporarily stored as an image signal in an image memory (not shown).
[0017]
As described above, the image of the document D placed on the document table 15 is imaged by the CCD sensor 14 for each line along the first direction in which the mirror 18a is extended. Is converted into, for example, an 8-bit digital image signal indicating the density of the image.
[0018]
The printer unit 20 includes an optical device 21 as an exposure device, which will be described later with reference to FIGS. 2 and 3, and an electrophotographic image forming unit 22 capable of forming an image on a recording paper P as an image forming medium. Have.
[0019]
The image forming unit 22 is rotated by the main motor described with reference to FIG. 3 so that the outer peripheral surface moves at a predetermined speed, and the laser beam L is irradiated from the optical device 21, whereby image data, that is, an image of the document D is applied. A drum-shaped photoconductor (hereinafter referred to as a photoconductor drum) 23 on which a corresponding electrostatic latent image is formed, a charging device 24 for applying a surface potential of a predetermined polarity to the surface of the photoconductor drum 23, and an optical device for the photoconductor drum 23. A developing device 25 that selectively supplies toner as a visualization material to the electrostatic latent image formed by the apparatus and develops the toner image formed on the outer periphery of the photosensitive drum 23 by the developing device 25. The transfer device 26 for transferring to the recording paper P, the recording paper P on which the toner image has been transferred by the transfer device, and the toner between the recording paper P and the photosensitive drum 23 are electrostatically absorbed by the photosensitive drum 23. The separation device 27 that releases (separates from the photosensitive drum 23) and the transfer residual toner remaining on the outer peripheral surface of the photosensitive drum 23 are removed, and the surface potential is supplied to the potential distribution of the photosensitive drum 23 by the charging device 24. And a cleaning device 28 for returning to the previous state. Note that the charging device 24, the developing device 25, the transfer device 26, the separation device 27, and the cleaning device 28 are arranged in order along the direction of the arrow in which the photosensitive drum 23 is rotated. Further, the laser beam L from the optical device 21 is irradiated to a predetermined position X on the photosensitive drum 23 between the charging device 24 and the developing device 25.
[0020]
An image signal read from the document D by the scanner unit 10 is converted into a print signal by an image processing unit (not shown) by, for example, gradation processing for contour correction or halftone display. The light intensity of the laser beam emitted from the semiconductor laser element described in the above is determined so that the electrostatic latent image can be recorded on the outer periphery of the photosensitive drum 23 to which a predetermined surface potential is applied by the charging device 24. The image is converted into a laser modulation signal for changing to any one of the non-recording intensity.
[0021]
Each semiconductor laser element shown below of the optical device 21 is intensity-modulated in accordance with the laser modulation signal described above, and records an electrostatic latent image at a predetermined position of the photosensitive drum 23 corresponding to predetermined image data. Emits light. The light from the semiconductor laser element is deflected in a first direction, which is the same direction as the reading line of the scanner unit 10, by a deflecting device described below in the optical device 21, and the outer periphery of the photosensitive drum 23. The predetermined position X is irradiated.
[0022]
Thereafter, when the photosensitive drum 23 is rotated in the direction of the arrow at a predetermined speed, the first carriage 11 and the second carriage 12 of the scanner unit 10 are moved along the document table 7 in the same manner as in the document table 7. The laser beam from the deflected semiconductor laser element is exposed on the outer circumference of the photosensitive drum 23 at predetermined intervals for each line.
[0023]
In this way, an electrostatic latent image corresponding to the image signal is formed on the outer periphery of the photosensitive drum 23.
The electrostatic latent image formed on the outer periphery of the photosensitive drum 23 is developed with toner from the developing device 25, conveyed to a position facing the transfer device 26 by the rotation of the photosensitive drum 23, and supplied from the paper cassette 29. One sheet is taken out by the paper roller 30 and the separation roller 31, and is transferred by the electric field from the transfer device 26 onto the recording paper P supplied with the timing aligned by the aligning roller 32.
[0024]
The recording paper P onto which the toner image has been transferred is separated together with the toner by the separation device 27 and guided to the fixing device 34 by the transport device 33.
The recording paper P guided to the fixing device 34 is discharged onto the tray 36 by the paper discharge roller 35 after the toner (toner image) is fixed by heat and pressure from the fixing device 34.
[0025]
On the other hand, the photosensitive drum 23 after the toner image (toner) is transferred to the recording paper P by the transfer device 26 is opposed to the cleaning device 28 as a result of the subsequent rotation, and the transfer residual toner (residual toner) remaining on the outer periphery. ) Is removed, and the state before the surface potential is supplied by the charging device 24 is returned to the initial state, and the next image formation becomes possible.
[0026]
By repeating the above process, a continuous image forming operation can be performed.
As described above, the document D set on the document table 15 is read by the scanner unit 10, and the read image information is converted into a toner image by the printer unit 20 and output to the recording paper P. Copied.
[0027]
FIG. 2 is a schematic diagram illustrating the internal structure of the optical device 21 shown in FIG.
As shown in FIG. 2, the optical device 21 is
A semiconductor laser element 41 for emitting a laser beam L having a predetermined wavelength;
A collimating lens 42 for adjusting the cross-sectional beam diameter of the laser beam L emitted from the semiconductor laser element 41, that is, the size of the beam spot, to a predetermined size;
A cylindrical beam that converges the laser beam L that has passed through the collimator lens 42 to a predetermined cross-sectional beam diameter in each of the scanning direction deflected and scanned by an optical deflector described below and the sub-scanning direction orthogonal to the deflected and scanned direction. Lens 43,
A diaphragm 44 which is disposed between the cylindrical lens 43 and the collimating lens 42 and gives a predetermined characteristic to the beam cross section of the laser beam L which is given a predetermined convergence through the cylindrical lens 43,
A polygonal mirror having a plurality of reflecting surfaces formed in a rotatable manner and a polygon motor 45A for rotating the polygon mirror, and a laser beam L given a predetermined convergence by the cylindrical lens 43 while rotating the polygon mirror An optical deflection device 45 that deflects (scans) by continuously reflecting toward the drum 23;
An angle θ formed between the photosensitive drum 23 and the laser beam L by the optical deflection device 45 is continuously changed with respect to the rotation direction of the polygon mirror, that is, the scanning direction. At the predetermined position on the outer peripheral surface of the photosensitive drum 23, that is, at the exposure position X shown in FIG. 1, the laser beam L irradiated from one end in the longitudinal (axis) direction of the photosensitive drum 23 to the other end is applied to the photosensitive drum. The first and second imaging lenses capable of providing convergence such that the angle θ and the focal length of the polygon mirror are a predetermined function so that a predetermined beam spot size is obtained at any position on the lens 23. Imaging optics 50 including 51 and 52, and
The laser beam L that has passed through the imaging optical system 50 is disposed on an equivalent exposure position that is a position obtained by extending the exposure position X of the photosensitive drum 23 in the axial (longitudinal) direction of the photosensitive drum 23, and the imaging optical system 50. A horizontal synchronization photodetector 53 that detects a timing for generating a horizontal synchronization signal by receiving a part of the laser beam L that has passed through and photoelectrically converting it;
Etc.
[0028]
A mirror capable of reducing the planar size of the optical device 21 is arranged between the first and second imaging lenses 51 and 52 and the photosensitive drum 23 as necessary. Also good.
[0029]
FIG. 3 is a schematic block diagram showing an example of a drive circuit of the copying apparatus 1 using the optical device 21 shown in FIG.
The CPU 101 as the main control device includes a ROM (read only memory) 102 in which predetermined operation rules and initial data are stored, a RAM 103 in which input control data is temporarily stored, image data from the CCD sensor 14 or This is a case where the image data supplied from the external apparatus is held, and the energization to the copying apparatus 1 is interrupted by the shared (image) RAM 104 that outputs the image data to the image processing circuit shown below and the battery backup. However, the NVM (nonvolatile memory) 105 that holds the data stored so far and the image data stored in the image RAM 104 are subjected to predetermined image processing and output to the laser driver described below. A processing device 106 and the like are connected.
[0030]
The CPU 101 also includes a laser driver 121 that drives the semiconductor laser element 41 of the optical device 21, a polygon motor driver 122 that drives a polygon motor 45 A that rotates a polygon mirror of the light deflection device 45, and a sheet of paper accompanying the photosensitive drum 23. A main motor driver 123 and the like for driving a main motor 23A for rotating the transport mechanism and the like are connected.
[0031]
The exposure operation will be briefly described below.
Based on a program stored in the ROM 101, the CPU 101 sends a predetermined drive signal to the polygon motor driver 122 and the main motor driver 123, that is, the PMCLK signal for controlling the rotation of the polygon motor and the polygon motor driver 122 to the polygon motor driver 122. A PMON signal for starting or stopping the rotation is sent to the main motor driver 123 as a reference clock MMCLK signal for controlling the rotational speed of the photosensitive drum 23 and an MMON signal for controlling ON / OFF of the motor 23A, respectively. .
[0032]
On the other hand, the semiconductor laser element 41 has a predetermined intensity at a predetermined timing in accordance with a laser drive current supplied from the laser driver 121 to the laser element 41 in response to a laser drive signal output from the CPU 101 to the laser driver 121. A laser beam L is emitted. The laser driver 121 reduces the intensity of the laser beam at an arbitrary position based on the image information developed in the bitmap in the image processing circuit 106 to such an extent that the photosensitive drum 23 does not form an electrostatic latent image. Therefore, a modulation signal (not shown) is also superimposed. Therefore, an electrostatic latent image corresponding to the presence / absence of image information is formed by the laser beam scanned by the polygon mirror of the light deflecting device 45 and irradiated in the axial direction of the photosensitive drum 23.
[0033]
4 shows an optical element arranged between the polygon mirror of the optical deflecting device 45 and the semiconductor laser element 41 in the optical device 21 shown in FIG. 4 is a schematic diagram illustrating a state of a laser beam L that passes through a cylindrical lens 43. FIG. FIG. 4 shows a cross section in the sub-scanning direction orthogonal to the direction in which the laser beam L is deflected by the polygon mirror of the light deflecting device 45 (scanned by rotating the polygon mirror). .
[0034]
As shown in FIG. 4, the laser beam L emitted from the laser element 41 is converted into a parallel beam parallel to at least the sub-scanning direction by the collimator lens 42. As already described with reference to FIG. 2, the laser beam L is converted into a parallel beam that is substantially parallel with respect to the scanning direction in which the polygon mirror is rotated.
[0035]
The laser beam L that has passed through the collimating lens 42 is incident on the cylindrical lens 43 through a diaphragm (light quantity setting member) 44 whose center in the sub-scanning direction is offset with respect to the center of the laser beam L. Note that the shape of the aperture of the diaphragm 44 is a predetermined shape that can provide the beam cross-sectional shape required when the laser beam L is imaged on the photosensitive drum 23. For example, FIG. As shown in any one of FIGS. 5B, an ellipse that is asymmetric with respect to the center in the scanning direction or a rectangle that is asymmetric with respect to the center in the scanning direction is set. The side set so that the amount of light passing through when the diaphragm 44 is offset is the distance from the scanning start end when the laser beam L is deflected and scanned by the polygon mirror of the optical deflector described below. Is matched to the larger side.
[0036]
That is, when the cross-sectional beam diameter of the laser beam fluctuates in relation to the deflection scanning by the optical deflecting device, the cross-sectional beam diameter fluctuation can be suppressed by reducing the area of the opening of the diaphragm 44. However, it is known that the cross-sectional beam diameter of the laser beam reaching the photosensitive drum 23 is increased by reducing the area of the opening of the diaphragm 44. For this reason, as shown in FIG. 2, the reflection point of the polygon mirror of the light deflection device 45 and the laser beam reflected by the polygon mirror and reaching the end portions (two places) in the axial direction of the photosensitive drum 23. For each, when vignetting has occurred on the polygon mirror surface, by setting the aperture opening on the side where the vignetting amount is large to be small and the aperture opening on the side where the vignetting amount is small being set large, at the main scanning end The increase in the beam diameter is prevented, and the beam diameter does not increase uniformly. When scanning the photosensitive drum scanning end, even if vignetting does not occur on the polygon mirror surface, the beam on the reflecting surface end surface side is reflected on the polygon mirror surface. Most The side where the distance between the outside angle light and the end face of the reflecting surface is large may be made larger on the aperture opening, and the side where the distance is smaller may be made smaller on the side where the distance is smaller.
[0037]
The cylindrical lens 43 is a compound lens in which a plastic cylindrical lens 43p is joined and integrated on the side of the glass cylindrical lens 43g facing the semiconductor laser element 41. The material of the plastic cylindrical lens 43p is formed of the same material as that of the first and second lenses 51 and 52 of the imaging optical system 50. Thereby, even if the temperature and humidity fluctuate at the position where the optical device 21 (copying device 2) is installed, the fluctuation of the cross-sectional beam diameter of the laser beam L is controlled to the minimum. Further, the glass cylindrical lens 43g of the cylindrical lens 43 is formed convex in the sub-scanning direction, and the plastic cylindrical lens 43p is formed concave in the sub-scanning direction. For this reason, the thickness of the plastic cylindrical lens 43p is minimum near the center in the sub-scanning direction and is maximum at both ends (in the sub-scanning direction). The plastic cylindrical lens 43p is processed by a low-cost molding process. Therefore, it is known that the shape error that may occur in the plastic cylindrical lens 43p is normally W-shaped as shown in FIG. 10 in the sub-scanning direction.
[0038]
Next, the relationship between the diameter of the polygon mirror of the light deflector 45, the length of each of the plurality of reflecting surfaces of the polygon mirror in the scanning direction, and the laser beam L passing through the imaging optical system 50 will be described.
[0039]
FIG. 6 is a schematic diagram showing the diameter of the polygon mirror 45a of the light deflecting device 45 and the state in which the laser beam L that has passed through the cylindrical lens 43 is reflected.
FIG. 6A shows a state in which the laser beam L is reflected by a polygon mirror 45a having, for example, six reflecting surfaces and a diameter of a circle circumscribing the connection point of the reflecting surfaces being 66 mm. ) Shows a state where the laser beam L is reflected by the polygon mirror 45a in which the reflection surface has six surfaces as shown in FIG. 6A and the diameter of the circle circumscribed by the connection point of the reflection surface is 40 mm. Each is shown schematically.
[0040]
As shown in FIG. 6B, when the cross-sectional beam diameter of the laser beam L, the optical path, or the angle toward the polygon mirror 45a are the same, the scanning method on each reflecting surface of the polygon mirror 45a. For As the size (length) of the laser beam becomes smaller (shorter), the laser beam L reflected at each connection point and the adjacent reflecting surface is also guided to the imaging optical system 50. In this case, the laser beam L reflected at the connection point of each reflection surface and the adjacent reflection surface is incident on the imaging optical system 50 due to vignetting at the connection point of each reflection surface and the adjacent reflection surface. The cross-sectional beam diameter is greatly changed, and the light intensity is also reduced.
[0041]
As described above, the laser beam L reflected by the connection point of the reflection surface and the adjacent reflection surface is reduced in light intensity and changed in beam diameter due to vignetting, so that the photosensitive drum is changed. 23, it deviates from a state where an electrostatic latent image can be provided. However, it is possible to provide the timing used for the horizontal synchronization signal to the horizontal synchronization detection photodetector 53 arranged at the position shown in FIG.
[0042]
In this case, the light receiving sensitivity of the horizontal synchronization detecting photodetector 53 is optimized in accordance with the light intensity and cross-sectional beam diameter of the laser beam L that is diffused due to vignetting by the polygon mirror 45a. For example, the change in the beam diameter due to vignetting can be easily obtained by measurement as shown in FIGS.
[0043]
7 and 8, the reflection surface of the polygon mirror 45a of the light deflecting device 45 is six, and the effective length of the photosensitive drum 23 is set so as to allow the length in the longitudinal direction (297 mm) of A4 size paper. The result of measuring the cross-sectional beam diameter of the laser beam L that has passed through the first and second imaging lenses 51 and 52 of the imaging optical system 50 at a position corresponding to the photosensitive drum 23 is shown.
[0044]
As is apparent from FIG. 7, it is recognized that the cross-sectional beam diameter increases rapidly at one end in the scanning direction. On the other hand, as shown in FIG. 8, the variation of the cross-sectional beam diameter in this example is relatively small.
[0045]
For this reason, the horizontal synchronization detection photodetector 53 is arranged at a predetermined position in the scanning direction, for example, at a position corresponding to −160 mm on the photosensitive drum 23, and the image area is changed from −150 mm to +147 mm. The incident timing of the laser beam L used for the horizontal synchronizing signal can be detected without being affected by the vignetting caused by the connection points of the respective reflecting surfaces of the polygon mirror 45a of the deflecting device 45, and a uniform and small beam in the image area. A diameter is obtained and a good image is obtained.
[0046]
FIG. 9 is a schematic diagram showing the degree of fluctuation of the light intensity of the laser beam L at a position corresponding to the imaging position of the photosensitive drum 23.
As shown in FIG. 9, it can be seen that the light intensity of the laser beam L decreases in relation to the scanning direction, at both ends, particularly at the outer portion from −155 mm where vignetting occurs due to the polygon mirror 45a. However, as described above, it is possible to detect the incident timing of the laser beam L that can be used as a horizontal synchronization signal by setting the sensitivity of the horizontal synchronization detection photodetector 53 to be optimal in advance.
[0047]
As described above, even when the diameter of the polygon mirror 45a of the light deflecting device 45 is reduced, the position of the horizontal synchronization detecting photodetector 53 (see FIG. 2) in accordance with the characteristics shown in FIGS. The laser beam L for obtaining the horizontal synchronization signal can be obtained even when the beam diameter and the light intensity of the laser beam L fluctuate due to the vignetting at the connecting portions of the reflecting surfaces. Can be detected. That is, the polygon mirror 45a can be reduced in size. Thereby, noise and vibration are reduced. Further, by reducing the size of the polygon mirror 45a, the size of the polygon mirror motor 45A for rotating the mirror can be reduced, and the output can be reduced.
[0048]
Incidentally, as shown in FIG. 4, the position where the laser beam L passes through the cylindrical lens 43 in the pre-deflection optical system 40 is set substantially at the center in the sub-scanning direction. Hereinafter, a case where the laser beam L passing through the cylindrical lens 43 moves in the sub-scanning direction will be considered.
[0049]
FIG. 10 shows the shape error of the plastic cylindrical lens 43p of the cylindrical lens 43 and the passage of the laser beam L when the laser beam L passes through the center of the cylindrical lens 43 in the sub-scanning direction as shown in FIG. This shows the relationship with the position. When the shape error of the plastic cylindrical lens 43p is indicated by the curve in FIG. 10, when the laser beam L passes through the approximate center in the sub-scanning direction indicated by the diagonal lines, the shape error is The laser beam L contributes approximately to the target and approximately to the arc in the sub-scanning direction. In this case, there is only an effect of changing the radius of curvature, and if the cylindrical lens is moved in the direction of the light beam and the focus is adjusted, the aberration does not increase, and the beam shape at the position of the photosensitive drum 23 is as shown in FIG. It can be seen that there are only slight side lobes (the design values are not inferior to those shown in FIG. 12 for comparison).
[0050]
On the other hand, as shown by the cross diagonal lines in FIG. 10, when the passing position of the laser beam L is different from the center of the plastic cylindrical lens 43p, the lens surface shape in the sub-scanning direction becomes asymmetrical. It can be seen that the degree of side lobes in the directional beam shape increases significantly as shown in FIG.
[0051]
As described above, when the pre-deflection optical system 40 including the plastic-molded cylindrical lens 43p, which often has a shape error in the sub-scanning direction, is used, the laser beam L is approximately circular with a symmetrical shape error. By passing the region, that is, the vicinity of the center in the sub scanning direction, it is possible to prevent the influence of the shape error of the cylindrical lens in the sub scanning direction from adversely affecting the image on the photosensitive drum. In other words, even if the tolerance of the shape error of the lens surface of the cylindrical lens is loosened, the management range of available lenses can be expanded by optimizing the position of the laser beam L passing through the lens. This indicates that the molding margin is widened and the cost of the lens can be reduced. The shape error of the cylindrical lens is minimized in a region where the variation rate of the thickness of the lens is small, that is, in the vicinity of the center of the lens in the sub-scanning direction. By providing a mechanism capable of adjusting the position in the scanning direction, it is possible to widen the management range of available lenses and reduce the component cost.
[0052]
【The invention's effect】
As described above, according to the optical device of the present invention, the beam is vignetted on the end face of the polygon mirror in the entire scanning region by the diaphragm set to be asymmetrical elliptical or rectangular with respect to the center in the scanning direction. Affected by And a uniform and small beam diameter can be obtained. Thereby, the fluctuation of the cross-sectional beam diameter of the light beam guided to the photosensitive drum is reduced.
[0053]
In addition, the horizontal synchronization detection photodetector is arranged at a predetermined position in the scanning direction, for example, at a predetermined position of the end of the photosensitive drum in the axial direction, at a position where the beam diameter increases, so that the image center region Then, it is possible to detect the incident timing of the laser beam L used for the horizontal synchronization signal without being affected by the vignetting caused by the connection points of the respective reflecting surfaces of the polygon mirror of the light deflector. Therefore, the size of the polygon mirror can be reduced and the cost can be kept low.
[0054]
Further, when a pre-deflection optical system including a plastic-molded cylindrical lens, which often involves a shape error in the sub-scanning direction, the laser beam L has a small shape error and an approximately small arc, that is, the center in the sub-scanning direction. By passing the vicinity, it is possible to prevent the influence of the shape error of the cylindrical lens in the sub-scanning direction from adversely affecting the image on the photosensitive drum. As a result, even if the tolerance of the shape error of the lens surface necessary for the lens surface of the cylindrical lens is loosened, the management range of available lenses can be expanded by optimizing the position of the laser beam L passing through the lens. Thus, the cost of the lens can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a digital copying apparatus (image forming apparatus) to which an embodiment of the present invention is applied.
FIG. 2 is a schematic diagram showing an example of an optical device incorporated in the copying apparatus shown in FIG.
FIG. 3 is a schematic block diagram for explaining a control block of the optical device shown in FIG. 2;
4 is a schematic view showing a passing position of a laser beam L in a cross-sectional direction of a cylindrical lens of the optical apparatus shown in FIG.
5 is a schematic view showing a state in which the diaphragm of the optical device shown in FIG. 2 is viewed from a direction orthogonal to the direction in which a laser beam L travels.
6 is a schematic diagram illustrating the diameter of a polygon mirror and the state of reflection of a laser beam in the optical deflection device of the optical device shown in FIG.
7 is a reflection surface of the polygon mirror of the optical deflector of the optical device shown in FIG. 2, the circumscribed circle has a diameter of 40 mm, and the effective length of the photosensitive drum is the length in the longitudinal direction of A4 size paper. Is the result of measuring the cross-sectional beam diameter in the scanning direction of the laser beam L that has passed through the first and second imaging lenses of the imaging optical system at a position corresponding to the photosensitive drum Graph showing.
FIG. 8 shows the reflection surface of the polygon mirror of the optical deflector of the optical device shown in FIG. 2, the diameter of the circumscribed circle is 40 mm, and the effective length of the photosensitive drum is the length in the longitudinal direction of A4 size paper. Is the result of measuring the cross-sectional beam diameter in the scanning direction of the laser beam L that has passed through the first and second imaging lenses of the imaging optical system at a position corresponding to the photosensitive drum Graph showing.
9 shows the optical intensity of the laser beam L at a position corresponding to the imaging position of the photosensitive drum under the condition that the cross-sectional beam diameter shown in FIGS. 7 and 8 can be provided in the optical device shown in FIG. A graph showing the degree of fluctuation.
10 is a graph showing a relationship between a shape error of a plastic cylindrical lens of the cylindrical lens of the optical device shown in FIG. 2 and a passing position of a laser beam L. FIG.
11 is a graph showing the degree of fluctuation of the beam diameter when the laser beam L passes through the approximate center in the sub-scanning direction of the plastic cylindrical lens in the optical apparatus shown in FIG.
12 is a graph showing the design theoretical value, which is the degree of variation of the beam diameter when the laser beam L passes through the approximate center in the sub-scanning direction of the plastic cylindrical lens in the optical apparatus shown in FIG.
13 is a graph showing the degree of fluctuation of the beam diameter when the laser beam L passes through a position at a predetermined distance from the vicinity of the center in the sub-scanning direction of the plastic cylindrical lens in the optical apparatus shown in FIG.
[Explanation of symbols]
1 ... Digital copier,
10: Scanner unit,
11: first carriage,
14 ... CCD sensor,
20 ・ ・ ・ Printer section,
21 ・ ・ ・ Optical device,
22 ... Image forming section,
23 ... photosensitive drum,
23A ... main motor,
32 ... Aligning roller,
40: Pre-deflection optical system,
41... Semiconductor laser element,
42 ... collimating lens,
43 ・ ・ ・ Cylindrical lens,
44 ・ ・ ・ Aperture,
45... Optical deflection device,
45A ... polygon motor,
50... Imaging optical system,
51... First imaging lens,
52... Second imaging lens,
53... Photodetector for horizontal synchronization detection,
101... CPU
102... ROM
103 ... RAM,
104... Shared (image) memory,
105 ... NVM (nonvolatile memory),
106 Image processing apparatus
111... Reference clock generation circuit,
121 ・ ・ ・ Laser driver,
122... Polygon motor driver,
123: Main motor driver.

Claims (7)

A first optical member that gives a predetermined optical characteristic to the light beam emitted from the light source, and a second optical beam that focuses the light beam given the predetermined optical characteristic by the first optical member in the first direction. And a reflecting surface formed to be rotatable about the rotation axis along the first direction, and the reflecting surface is rotated in a second direction orthogonal to the first direction. Scanning means for scanning the light beam, imaging means for passing the light beam scanned by the scanning means to form an image on the scanning object, and position of the light beam scanned in the second direction by the scanning means An optical device having a photodetector for detecting a light beam to identify
The first optical member includes a first lens having a substantially equal power to each of the first direction and the second direction,
The second optical member is a lens glass cylindrical lens and the plastic cylindrical lens are integrated, the second providing the first person only convergence in direction of the first lens light beam passing through the a lens, has an opening comprising a predetermined shape when viewed from the third direction perpendicular to the respective first and second directions, between the first and second lens, the first lens The light beam that has passed through is asymmetric with respect to the first direction orthogonal to the second direction, which is the direction in which the convergence is given by the second lens , and from the scanning start end when the light beam is scanned by the scanning means the side where the distance is large, is arranged to pass light intensity increases, the light intensity of the light beam directed toward the second lens and a light amount setting member for setting the arbitrary ratio, said first optical member La of the light beam, the second lens, the light beam that emits the second optical member with passing a substantially central region in the second direction, the beam diameter on the reflection surface of the scanning means , Control the beam diameter of the light beam to be smaller than the reflective surface,
The photodetector detects a light beam in an area other than an image area where an electrostatic latent image is formed on a scanning object by being reflected by a connection point of the reflection surface of the scanning unit and an adjacent reflection surface. And an optical device that detects a light beam reflected by a connection point of the reflection surface of the scanning unit and an adjacent reflection surface. A first optical member that gives a predetermined optical characteristic to the light beam emitted from the light source, and a second optical beam that focuses the light beam given the predetermined optical characteristic by the first optical member in the first direction. And a reflecting surface formed to be rotatable about the rotation axis along the first direction, and the reflecting surface is rotated in a second direction orthogonal to the first direction. Scanning means for scanning the light beam, imaging means for passing the light beam scanned by the scanning means to form an image on the scanning object, and position of the light beam scanned in the second direction by the scanning means An optical device having a photodetector for detecting a light beam to identify
The first optical member includes a first lens having a substantially equal power to each of the first direction and the second direction,
It said second optical member includes a second lens which gives only convergence in the first direction of the light beam passing through the first lens, between the first and second lens, the first lens The light beam that has passed through is asymmetric with respect to the first direction orthogonal to the second direction, which is the direction in which the convergence is given by the second lens , and from the scanning start end when the light beam is scanned by the scanning means the side where the distance is large, is arranged to pass light amount is large, the light amount setting member for setting the light intensity of the light beam toward the second lens in any proportion, having a first optical member The beam diameter on the reflecting surface of the scanning means is compared with the light beam that passes through the second lens in the vicinity of the center of the second direction and exits the second optical member. Smaller than reflective surface To control the beam diameter Urn light beam,
The photodetector detects a light beam in an area other than an image area where an electrostatic latent image is formed on a scanning object by being reflected by a connection point of the reflection surface of the scanning unit and an adjacent reflection surface. And an optical device that detects a light beam reflected by a connection point of the reflection surface of the scanning unit and an adjacent reflection surface. A first optical member that gives a predetermined optical characteristic to the light beam emitted from the light source, and a second optical beam that focuses the light beam given the predetermined optical characteristic by the first optical member in the first direction. And a reflecting surface formed to be rotatable about the rotation axis along the first direction, and the reflecting surface is rotated in a second direction orthogonal to the first direction. Scanning means for scanning the light beam, imaging means for passing the light beam scanned by the scanning means to form an image on the scanning object, and position of the light beam scanned in the second direction by the scanning means An optical device having a photodetector for detecting a light beam to identify
The first optical member includes a first lens having a substantially equal power to each of the first direction and the second direction,
Said second optical member includes a glass cylindrical lens and a plastic cylindrical lens is a composite lens formed integrally, only the first direction of the light beam passing through the first lens A second lens that provides convergence; an aperture that has a predetermined shape when viewed from a third direction orthogonal to each of the first direction and the second direction; and In the meantime, the light beam that has passed through the first lens is asymmetric with respect to the first direction orthogonal to the second direction, which is the direction in which the convergence is given by the second lens , and the light beam is scanned by the scanning means. the side where the distance increases from the scanning start end of the time that includes being arranged to pass light amount is large, the light amount setting member for setting the light intensity of the light beam toward the second lens in any ratio, the Relates the second direction light beam which has passed through the first lens is the direction to be converged, the light beam that the light beam passes through the vicinity of the center in the same direction, and emits the second optical member, Controlling the beam diameter of the light beam so that the beam diameter on the reflecting surface of the scanning means is smaller than the reflecting surface;
The photodetector detects a light beam in an area other than an image area where an electrostatic latent image is formed on a scanning object by being reflected by a connection point of the reflection surface of the scanning unit and an adjacent reflection surface. And an optical device that detects a light beam reflected by a connection point of the reflection surface of the scanning unit and an adjacent reflection surface.   4. The optical apparatus according to claim 1, wherein the plastic lens of the second lens of the second optical means is positioned on the light source side.   3. The optical apparatus according to claim 2, wherein the second lens of the second optical means has a plastic lens integrated on the light source side. 2. The light amount setting member is positioned so that an opening is reduced on a side where the amount of vignetting is large when vignetting occurs at a scanning end of a light beam scanned by the scanning unit. 4. The optical device according to any one of 3 to 3. The optical detector according to any one of claims 1 to 3, wherein the photodetector has a light receiving sensitivity matched to a connection point of the reflecting surface of the scanning unit and a light beam reflected on an adjacent reflecting surface. apparatus.

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