CN102749706B - Optical scanning apparatus and imaging apparatus - Google Patents

Optical scanning apparatus and imaging apparatus Download PDF

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Publication number
CN102749706B
CN102749706B CN201210113592.9A CN201210113592A CN102749706B CN 102749706 B CN102749706 B CN 102749706B CN 201210113592 A CN201210113592 A CN 201210113592A CN 102749706 B CN102749706 B CN 102749706B
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scanning
light
scanning apparatus
rotating mirror
polygonal rotating
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CN102749706A (en
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增田宪介
今井重明
三宅信辅
仲村忠司
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Ricoh Co Ltd
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Ricoh Co Ltd
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  • Fax Reproducing Arrangements (AREA)

Abstract

The present invention relates to an optical scanning apparatus and an imaging apparatus, in order to overcome the defect of unequal scanning line space and increase image quality under the condition that the subsidiary scanning image surface curves. The optical scanning apparatus (100) comprises a light source (1), a pillar mirror (4) and a scanning mirror (6), and when the main and subsidiary scanning directions of a rotation polygonal mirror are respectively a first direction and a second direction, the relations are satisfied that alpha2<alpha1 and alpha3 and beta2<beta1 and beta3, or, alpha2>alpha1 and alpha3, in a third direction perpendicular to the first and second directions, wherein the alpha1, alpha2 and alpha3 respectively represents a distance from a rotation center to a reflection position at the beginning, middle and end of scanning, and beta1,beta2, beta3 respectively represents a distance from an imaging surface to a paraxial focus converged by light beams in the second direction at the beginning, middle and end of scanning.

Description

Light scanning apparatus and imaging device
Technical field
The present invention relates to light scanning apparatus and imaging device, be specifically related to the light scanning apparatus that can be used for the imaging devices such as laser digital duplicating machine, laser printer or facsimile recorder.
Background technology
Widely use optical imaging device when utilizing electrofax mode record image, and in such imaging device, be typically provided with the light scanning apparatus carrying out photoscanning with laser.Light scanning apparatus when forming sub-image usually in the following ways, namely LASER Light Source Emission Lasers is used, this light is by after the polarizer deflections such as polygonal rotating mirror, inciding outer surface has in the photosensitive drums of photosensitive property, now, polarizer scans photosensitive drums along the main scanning direction being parallel to photosensitive drum shaft, meanwhile, this photosensitive drums is rotated along sub scanning direction centered by axle, thus forms sub-image on photosensitive drums outer surface.
Trace interval is one of key property of above-mentioned light scanning apparatus.So-called sweep trace refers to the track while scan that luminous point is formed, and trace interval refers to the distance between adjacent scanning lines.If trace interval is indefinite, that is, if trace interval is unequal, then can deform on the image write with photoscanning.
Obtain good image write, need to reduce trace interval as far as possible unequal.The unequal main cause of trace interval is to tilt for the polygonal rotating mirror minute surface as light deflector.Specifically, it is exactly the rotation axis that the deflecting reflecting face of polygonal rotating mirror is not exclusively parallel to polygonal rotating mirror, deflected beam moves on sub scanning direction with different deflecting reflecting faces, thus the luminous point image space in surface to be scanned is changed along sub scanning direction, cause trace interval unequal.
For the problems referred to above, such as, in patent documentation 1 (TOHKEMY clear 63-313113 publication), describe a kind of piezo electrics element make minute movement to compensate the method for optical axis movement to make collimating mirror.In addition, patent documentation 2 (TOHKEMY clear 61-212818 publication) also discloses a kind of technical scheme, the program two bundle laser that two LASER Light Source occur form a sweep trace, by changing this two bundle laser power separately, the center of gravity controlling to synthesize light beam changes along with the variation of trace interval.
And then the tilt data describing a kind of certain reflecting surface based on polygonal rotating mirror in patent documentation 3 (JP Laid-Open 4-200065 publication) finely tunes to compensate the method for density unevenness to laser light quantity.In addition, the technical scheme that patent documentation 4 (TOHKEMY 2006-150772 publication) describes is, irradiation interval data and input image data according to representing light irradiation position interval obtain an interval, carry out light quantity compensation based on this interval data, the compensation of this light quantity is only limitted to the light-emitting component beyond the light-emitting component of the input image data between non-luminescent data that correspondence is clamped in more than 2.
But, polygonal rotating mirror minute surface tilt compensation method described in above-mentioned patent documentation 1 and 2 needs the element such as piezoelectric element or light source, and increase element and can bring the problems such as manufacturing cost rising, also need the control system of minute surface slope compensation in addition, this not only can make structure become complicated, but also can cause discontinuous
The problems such as the line of (being formed with isolated point or line) image or some instability.
Summary of the invention
In view of the above problems, the invention provides a kind of do not need other brought into optical element or control system, just can overcome the trace interval that minute surface tilts to cause unequal, can operating stably light scanning apparatus and possess the imaging device of this light scanning apparatus.
In order to achieve the above object, the invention provides there is following technical scheme.
(1) first, the invention provides a kind of light scanning apparatus, comprising: light source; First optical system, for light beam that described light source is launched on polygonal rotating mirror with line as imaging; And, second optical system, for by the light beam after the deflection of described polygonal rotating mirror on imaging surface with point as imaging, it is characterized in that, when the main scanning direction sub scanning direction carrying out deflection scanning with described polygonal rotating mirror is respectively first direction and second direction, and with simultaneously perpendicular to the direction of this first direction and this second direction for third direction time, this light scanning apparatus meets following relational expression:
α 2 < α 1, α 3 and β 2 < β 1, β 3, or,
α 2 > α 1, α 3 and β 2 > β 1, β 3,
Wherein, α 1, α 2, α 3 scanning be respectively when polygonal rotating mirror carries out deflection scanning starts, scan in the middle of, the end of scan time beam reflection position from the center of rotation of polygonal rotating mirror to polygonal rotating mirror distance, β 1, β 2, β 3 scanning be respectively when polygonal rotating mirror carries out deflection scanning starts, scan in the middle of, the end of scan time from imaging surface to sub scanning direction on light beam convergence paraxial foci position between distance.
(2) feature of the light scanning apparatus according to above-mentioned (1) is also, in this light scanning apparatus, following relational expression is set up,
&gamma; 2 - &gamma; 1 2 &le; &beta; 1 - &beta; 2 &le; &gamma; 2 - &gamma; 1 And &gamma; 2 - &gamma; 3 2 &le; &beta; 3 - &beta; 2 &le; &gamma; 2 - &gamma; 3
Wherein, the scanning that γ 1, γ 2, γ 3 are respectively described starts, scan in the middle of, the end of scan time described second direction the degree of depth.
(3) feature of the light scanning apparatus according to above-mentioned (1) is also, this light scanning apparatus meets following relational expression,
α 2 < α 1, α 3 and β 2 < β 1, β 3.
(4) feature of the light scanning apparatus according to above-mentioned (1) is also, when with the light going direction of described third direction for positive dirction, and when being negative direction with opposite direction, described scanning start and the described end of scan time described second direction on paraxial foci position than described scanning in the middle of time described second direction on paraxial foci position be more positioned at positive dirction side.
(5) feature of the light scanning apparatus according to above-mentioned (4) is also, the paraxial foci position in the described second direction when paraxial foci position in described second direction when described scanning starts and the described end of scan is consistent.
(6) feature of the light scanning apparatus according to above-mentioned (1) is also, described second direction described scanning start and the end of scan time beam waist position than respective paraxial foci position more near imaging surface side.
(7) feature of the light scanning apparatus according to above-mentioned (1) is also, described second optical system is formed with an optical element, and this optical element has energy on described first direction and described second direction.
(8) feature of the light scanning apparatus according to above-mentioned (1) is also at least have light source described in two or more.
(9) feature of the light scanning apparatus according to above-mentioned (1) is also, described second optical system has meniscus shape, and this meniscus shape protrudes towards described light going direction in this second direction.
(10) secondly, the invention provides a kind of imaging device, comprising multiple image carrier and light scanning apparatus, this light scanning apparatus scans with according to the light beam after the modulate image information on described multiple image carrier, it is characterized in that, this optical scanning device is set to the light scanning apparatus in above-mentioned (1) ~ (9) described in any one technical scheme.
The feature of imaging device of the present invention is the light scanning apparatus comprising the invention described above, and this light scanning apparatus can carry out modulated beam of light for the image information of different image carriers and different image carrier, and scans with this light beam through ovennodulation.
Effect of the present invention is in the scope that beam diameter Quality Down does not occur, can improve the subscan curvature of the image unequal relative to trace interval, improves image quality.
Accompanying drawing explanation
Fig. 1 is the primary structure schematic diagram of the embodiment of a routine light scanning apparatus involved in the present invention.
Fig. 2 is the primary structure schematic diagram of the embodiment of another routine light scanning apparatus involved in the present invention.
Fig. 3 is the primary structure schematic diagram of a routine imaging device involved in the present invention.
Fig. 4 is for illustration of image space sagging schematic diagram occurs in polygonal rotating mirror.
Fig. 5 A and Fig. 5 B is the schematic diagram of relation between the position of deflecting reflecting face and the position of surface to be scanned, wherein Fig. 5 A is the example that image space and surface to be scanned are consistent, and Fig. 5 B is the sagging example causing the unequal generation of trace interval of the image space of polygonal rotating mirror.
The schematic diagram of the relation of the rotation axis of image height and polygonal rotating mirror and the spacing (sag of chain) of reflection spot in Fig. 6 A reading scan optical system, Fig. 6 B is the curvature of the image performance plot of sub scanning direction.
Fig. 7 A and Fig. 7 B is the central image height of scanning optics and the depth curve figure of periphery image height on the main scanning direction of embodiment 1 and sub scanning direction respectively.
Fig. 8 is the contrast table of the incident angle in the scanning optics of comparative example 1 and comparative example 1 in surface to be scanned.
Fig. 9 is the optical texture schematic diagram of light scanning apparatus.
Figure 10 is the catalog data of the scanning optics in embodiment 1 between polygonal rotating mirror and surface to be scanned.
Figure 11 is the main scanning direction of the scanning mirror plane of incidence of embodiment 1 and the coefficient complete list of sub scanning direction.
Figure 12 is the main scanning direction of the scanning mirror surface of emission of embodiment 1 and the coefficient complete list of sub scanning direction.
Figure 13 A is the curvature of the image performance plot of embodiment 1, and Figure 13 B is uniform velocity performance plot.
Figure 14 is the catalog data of the scanning optics in comparative example 1 between polygonal rotating mirror and surface to be scanned.
Figure 15 is the main scanning direction of the scanning mirror plane of incidence of comparative example 1 and the coefficient complete list of sub scanning direction.
Figure 16 is the main scanning direction of the scanning mirror surface of emission of comparative example 1 and the coefficient complete list of sub scanning direction.
Figure 17 A is the curvature of the image performance plot of comparative example 1, and Figure 17 B is uniform velocity performance plot.
Figure 18 A and Figure 18 B is the central image height of scanning optics and the depth curve figure of periphery image height on the main scanning direction of comparative example 1 and sub scanning direction respectively.
Description of symbols:
1 light source, 2 coupling mirrors, 3 apertures, 4 cylindricality mirrors, 5 polygonal rotating mirrors, 5a deflecting reflecting face, 5b rotation axis, 6 scanning mirrors, 7 catoptrons, 8 photoreceptors (surface to be scanned), 9 catoptrons, 10 imaging lens, 11 photo detectors, 100 light scanning apparatuss, 1000 imaging devices, 1110 image carriers, 1121 charging rollers, 1131 developing apparatuss, 1141 transfer rolls, 1151 cleaning devices, 1161 fixing devices, 1171 light scanning apparatuss, 1181 paper feeding cassettes, 1191 registration rollers pair, 1201 paper feed rollers, 1211 transfer paper transport paths, 1221 exit rollers pair, 1231 storehouse dishes, LB laser beam, P transfer paper.
Embodiment
Below utilize embodiment shown in the drawings to describe structure of the present invention in detail.
The light scanning apparatus 100 of present embodiment comprises light source 1, first optical system and the second optical system.First optical system and line are as imaging optical system, formed with cylindrical mirror 4, for light beam that light source is launched on rotation polygonal rotating mirror and polygonal rotating mirror 5 with line as imaging, second optical system and scanning optics, formed with scanning mirror 6, for by through rotation the light beam after polygonal rotating mirror deflection scanning in image planes with point as imaging.Main scanning direction in this light scanning apparatus 100 after polygonal rotating mirror deflection scanning is for first direction, sub scanning direction is second direction, when being simultaneously third direction perpendicular to the direction of first direction and second direction, this light scanning apparatus meets following relational expression: α 2 < α 1, α 3 and β 2 < β 1, β 3, or, α 2 > α 1, α 3 and β 2 > β 1, β 3, at this, α 1, α 2, the scanning that α 3 is respectively when polygonal rotating mirror 5 carries out deflection scanning starts, in the middle of scanning, distance beam reflection position from the center of rotation of polygonal rotating mirror to polygonal rotating mirror during the end of scan, β 1, β 2, the scanning that β 3 is respectively when polygonal rotating mirror 5 carries out deflection scanning starts, in the middle of scanning, during the end of scan from imaging surface to sub scanning direction on light beam assemble paraxial foci position between distance.In the present embodiment, main scanning direction refers to the direction of the deflection scanning of polygonal rotating mirror 5, and sub scanning direction refers to the direction of the center of rotation of polygonal rotating mirror 5, and the direction vertical with sub scanning direction with main scanning direction and light direction of illumination refer to third direction simultaneously.
" light scanning apparatus 1 "
Fig. 1 is the schematic diagram of the primary structure of the embodiment of a routine light scanning apparatus involved in the present invention.What Fig. 1 showed is single beam mode light scanning apparatus 100, launches diverging light from semiconductor laser and light source 1, and this light beam is converted into weak diversity light beam by beam pattern after coupling mirror 2.
Through the light beam of coupling mirror 2 when by the peristome of aperture 3, light beam peripheral part is blocked and is shaped, and then incides line as imaging optical system and cylindricality mirror 4.
Cylindricality mirror 4 does not have energy on the direction being parallel to main scanning direction, and at sub scanning direction, there is positive energy, like this, incident beam is only assembled on sub scanning direction, thus near the deflecting reflecting face of the polygonal rotating mirror 5 of light deflector, light beam assembles growth line picture along main scanning direction.
The constant velocity rotation of the light beam accompanying rotation polygonal mirror 5 reflected by the deflection plane of polygonal rotating mirror 5 and after being deflected by constant angular velocity, through a slice scanning mirror 6 forming scanning optics, after then bending light path by catoptron 7, converge on the photoconductivity photoreceptor 8 (surface to be scanned 8) of formation surface to be scanned entity, form luminous point (some picture), scanning surface to be scanned.
Deflected beam, before starting to carry out photoscanning to photoreceptor 8 surface, is converged on photo detector 11 by imaging lens 10 after catoptron 9 reflects.Output signal after photo detector 11 light, according to the output of this photo detector 11, decide the write start time of photoscanning.
Scanning optics is used for the light beam after light deflector 5 deflects to converge in surface to be scanned 8 to form luminous point, forms scanning optics in the example depicted in figure 1 with a slice scanning mirror.
" light scanning apparatus 2 "
Fig. 2 shows embodiment and the multiple beam mode light scanning apparatus 100 of another example light scanning apparatus involved in the present invention.
Light source in embodiment shown in Fig. 2 is semiconductor laser array, and the row light emitting source ch1 ~ ch4 equidistantly arranged with four is formed.Arrange along sub scanning direction at four light emitting sources of the semiconductor laser array of this display, also can adopt the semiconductor laser array that orientation is tilted relative to sub scanning direction.
Four light beams that four light source radiation shapes are launched are the long axis direction of the oval far-field pattern diversity light beam consistent with main scanning direction.Four light beams are incided after being coupled by same coupling mirror 2 in optical system after this.Each light beams form after being coupled can become weak diversity light beam or weak bandha light beam according to the optical characteristics of optical system after this, can also become parallel beam.
Four light beams are by being subject to the beam shaping of aperture 3 after coupling mirror 2, then under the effect of same line as imaging optical system and cylindricality mirror 4, collect separately on sub scanning direction, near the deflecting reflecting face of light deflector and polygonal rotating mirror 5, each light beams along separate imaging on sub scanning direction, shape growth line picture on main scanning direction respectively.
After polygonal rotating mirror 5 is driven and is rotated, the deflecting reflecting face being subject to this polygonal rotating mirror 5 deflects four light beams with constant angular velocity, the scanning optics that four light beams transmissions are formed with a slice scanning mirror 6 after overshoot, after then the light path of light beam is subject to catoptron 9 bending, be irradiated to the surface to be scanned 8 i.e. outer surface of photoreceptor 8, assemble on sub scanning direction respectively, form four luminous points separately, four sweep traces scan surface to be scanned 8 simultaneously.
Above-mentioned four beam steering light beams are through after scanning mirror 26, and a branch of light beam was wherein subject to the reflection of catoptron 9 before arriving scanning photoreceptor 8 surface, converged on photo detector 11 through eyeglass 10.Output detections signal after photo detector 11 light, and four light beams photoscanning write start time separately just depends on this output signal.
" imaging device "
Secondly the embodiment of the imaging device that one example is involved in the present invention is described.Fig. 3 is the schematic diagram of the primary structure of imaging device.
Imaging device 1000 shown in Fig. 3 possesses photonasty image carrier 1110, and it is in order to as cylindrical shape photoconductivity photoreceptor.
Above-mentioned image carrier 1110 surrounding arranges charging roller 1121, developing apparatus 1131, transfer roll 1141, cleaning device 1151.Be charging device at this with charging roller, in addition, can also with corona charging device as charging device.
Above image carrier 1110 and charging roller 1121, arrange light scanning apparatus 1171, this light scanning apparatus 1171 is the light scanning apparatus 100 of present embodiment, carries out photoscanning with laser beam LB.Between charging roller 1121 and developer roll 1131, light write, exposes.
Mark 1161 represents fixing device, mark 1181 represents paper feeding cassette, mark 1191 represents a pair registration roller, mark 1201 represents paper feed roller, mark 1211 represents transfer paper transport path, mark 1221 represents a pair exit roller, marks 1231 indicating panels, and mark P represents the transfer paper as recording medium sheet.
When imaging, the image carrier 1110 of photoconductivity photoreceptor does clockwise direction constant velocity rotation, and its surface is subject to charging roller 1121 and charges and uniform charged.Light scanning apparatus 1171 Emission Lasers light beam LB carries out light write on the surface at charged rear image carrier 1110, forms electrostatic latent image after exposure.Electrostatic latent image is negative sub-image, and its image section is exposed.Developing apparatus 1131 to this electrostatic latent image transfer printing, thus forms toner image on image carrier 1110.
Paper feeding cassette 1181 for placing transfer paper P can load and unload on the main frame of imaging device 1000, and as shown in the figure, under paper feeding cassette 1181 is in the state be installed on main frame, paper feed roller 1201 sucking-off is placed in one a uppermost transfer paper P.The front end of the transfer paper P that this is sucked out is clamped among a pair registration roller 1191.
This coordinates the toner image on image carrier 1110 to move to moment in transfer position to registration roller 1191, and transfer paper P is sent into the transfer roll 1141 as transfer roll.The transfer paper P being admitted to transfer section is overlapping with toner image, and be subject to transfer roll 1161 and act on, this toner image is electrostatically transferred on transfer paper P.Then, transfer paper P is sent to fixing device 1161, and in fixing device, toner image is fixed on transfer paper P, and then this transfer paper P is by transport road 1211, is rejected on storehouse dish 1231 by a pair exit roller 1221.
In transfer printing after toner image, cleaning device 1151 cleans image carrier 1110 surface, removes residual toner or paper powder etc.At this, excellent imaging can be obtained with the light scanning apparatus 100 of present embodiment as light scanning apparatus 1171.
And then the color image forming apparatus of tandem can be configured to, the i.e. multiple photonasty image carrier of spread configuration, photoscanning is carried out with the light scanning apparatus of each image carrier of correspondence, form assorted sub-image, and with developing apparatus by visual for these sub-images, and then overlap is transferred on transfer paper etc., obtains coloured image.Adopt above-mentioned light scanning apparatus 100 as each scanister in this color image forming apparatus, the imaging of excellence as described below can be obtained.
" scanning optics "
As mentioned above, trace interval is the key property of light scanning apparatus.The main cause of the unequal generation of trace interval is to tilt for the scanning plane of the polygonal rotating mirror 5 as light deflector.That is, if the deflecting reflecting face 5a of polygonal rotating mirror 5 is not exclusively parallel relative to the rotation axis of this polygonal rotating mirror 5, then deflected beam will be followed each deflection side and penetrated face 5a and be moved at sub scanning direction, the image space of the luminous point in surface to be scanned 8 is moved along sub scanning direction, thus causes trace interval unequal.
About the generation optically preventing trace interval unequal, there is following minute surface tilt compensation method, namely the light beam making light source launch near the deflecting reflecting face 5a of polygonal rotating mirror 5 along the upper imaging of the main sweep correspondence direction direction of corresponding main sweep face (from the light source 1 light path of surface to be scanned 8), shape growth line picture, makes near deflecting reflecting face 5a with scanned imagery optical system and surface to be scanned position is conjugate relation on subscan correspondence direction.The method can provide a kind of stable light scanning apparatus to solve minute surface tilt problem, and does not need to introduce new optical element and control system etc.
But, in polygonal rotating mirror 5, the rotation axis 5b of deflecting reflecting face and deflecting reflecting face deviate, and for this reason along with the rotation of deflecting reflecting face, the image space of above-mentioned line picture can depart from deflecting reflecting face, namely there is the problem of so-called image space sagging (sag, hereinafter also referred to as sagging).
The problems referred to above are described in detail see Fig. 4.Fig. 4 show polygonal rotating mirror 5 deflecting reflecting face 5a and from light source light beam (chief ray of light beam) L between position relationship.The deflecting reflecting face 5a of polygonal rotating mirror 5 along with rotating clockwise of this polygonal rotating mirror 5a from 5a (1) to 5b (1) and then change to 5c (1), to should the change of deflecting reflecting face of polygonal rotating mirror 5, the reflection position of the chief ray of light beam L also from M (-) to M (0) and then change to M (+).
From the light beam L of light source on reflection position M (0) with line as imaging., when this light beam L incides reflection position M (-) and M (+), depart between the image space of deflecting reflecting face 5a and line picture, the light beam also non-imaging when incidence reflection position M (-) and M (+) for this reason.
It is sagging that the departing from of above-mentioned deflecting reflecting face and reflection position is image space, it asymmetricly occurs in the both sides of the reflection position M (0) shown in Fig. 4 (in the diagram usually, the sag of chain being positioned at M (-) is greater than the sag of chain of M (+)), but can by the position relationship between adjustment polygonal rotating mirror 5 and an incident side optical system (cylindricality mirror), the sagging symmetry that is adjusted to occurred reflection position M (0) both sides occurs.In addition, scanned imagery optical system is set to the chief ray of light beam of the upper reflection of reflection position M (0) by sag of chain being 0 and the optical axis of scanned imagery optical system is consistent usually.
Fig. 5 display, by scanning mirror 6, is the state of conjugate relation between the position of deflecting reflecting face 5a and the position of surface to be scanned 8.
As shown in Figure 5A, the light beam reflected at reflection position p (0) is (on corresponding main scanning direction, long line picture and p (0) are consistent) because of above-mentioned conjugate relation, image space q (0) and surface to be scanned 8 are consistent.
If there is minute surface to tilt, when namely (representing to mark 5a ') when deflecting reflecting face 5a tilts relative to rotation axis 5b, for the conjugate relation between the position of deflecting reflecting face 5a and the position of surface to be scanned 8, the light beam that deflecting reflecting face 5a reflects roughly can be assembled in surface to be scanned 8.Now, requirement position (optical axis of Fig. 5) can not be departed from the position being subject to the sub scanning direction of light beam irradiation.
To this, as shown in Figure 5 B, the light beam reflected at reflection position p (1) due to the sagging impact of the image space that is subject to occurring in polygonal rotating mirror 5, once assemble in r (1) position after deflecting reflection.
In existing optical system, to each image height design main sweep shape, light beam is assembled in surface to be scanned 8.For this reason, from the q (1) that the divergent beams of r (1) will converge in surface to be scanned 8.
Now, the conjugate points of the reflection position p (1) of polygonal rotating mirror 5 is positioned at s (1) before surface to be scanned 8, like this, when minute surface occurring and tilting, that is, when deflecting reflecting face 5a tilts relative to rotation axis 5b
Time (representing to mark 5a '), although image space is identical with the q (1) do not occurred before minute surface tilts in surface to be scanned 8, the position on the subscan face of light beam irradiation then to+direction is moved.
This is that the sagging caused unequal problem of scan light spacing of image space occurs polygonal rotating mirror 5.With the light beam of normal incidence imaging surface in the optical system of multiple beam mode than single-beam optical system in be more prone to add further incident imaging surface at a certain angle.This tendency is particularly remarkable in the single lens optical system kept within bounds being subject to design parameter.
Specifically, such as same as the prior art in multiple beam optical system, when setting subscan image planes sag of chain is 0.5mm, the trace interval when minute surface tilt quantity of polygonal rotating mirror 5 is 90s is unequal reaches more than 70 μm.And when 1200dpi writes, because trace interval is 21 μm, will there is the image quality issues such as density unevenness in 1/3 variation of spacing in such a configuration.And in order to reduce density unevenness, preferred sweep span is unequal is less than 6 μm.
As mentioned above, the minute surface of polygonal rotating mirror 5 trace interval that tilts to cause is unequal to a great extent by the impact that the image space of polygonal rotating mirror is sagging.In order to obtain the sagging balance in imaging surface position between image height, usually need the main sweep immediate vicinity of incident light beam strikes to polygonal rotating mirror minute surface, to obtain left-right balance.Near central image height, polygonal rotating mirror minute surface and imaging surface become conjugate relation, and tilt even if now there is minute surface, trace interval is unequal also not obvious.But in periphery image height, due to sagging impact, the conjugate points of imaging surface one side leaves imaging surface position, like this, if occur that minute surface tilts in polygonal rotating mirror 5, sweep trace just can be caused unequal.
To this, the light scanning apparatus 100 of present embodiment changes the paraxial foci position of each image height according to the sag of chain of polygonal rotating mirror 5, sagging in order to the image space reducing polygonal rotating mirror 5 generation.
That is, start when setting scanning when polygonal rotating mirror 5 carries out deflection scanning, in the middle of scanning, distance beam reflection position from the center of rotation of polygonal rotating mirror to polygonal rotating mirror during the end of scan is respectively α 1, α 2, α 3, and the scanning set when polygonal rotating mirror 5 carries out deflection scanning starts, in the middle of scanning, during the end of scan from imaging surface to sub scanning direction on light beam assemble paraxial foci position between distance be respectively β 1, β 2, during β 3, meet following relational expression: α 2 < α 1, α 3 and β 2 < β 1, β 3, or, α 2 > α 1, α 3 and β 2 > β 1, β 3.
Above-mentioned light scanning apparatus 100 can by changing the subscan curvature of the image that in scanning optics, image height peripheral part occurs, and it is unequal by trace interval when reducing minute surface inclination, in the scope that beam diameter deterioration does not occur, unequally relative to sweep trace improve subscan curvature of the image, improve image quality.Fig. 6 A shows the relation of the rotation axis 5b of image height and polygonal rotating mirror 5 in the scanning optics of the light scanning apparatus 100 of present embodiment and the spacing (sag of chain) of reflection spot.Fig. 6 B shows the curvature of the image characteristic of sub scanning direction.
From Fig. 5 and Fig. 6, centered by near image height 0, along with trending towards image height peripheral part, sag of chain and the distance converging to the imaging surface on sub scanning direction are also tending towards becoming large gradually.In the example shown in Fig. 6, when image height be-163.5mm, 0,163.5mm time, distance between the rotation axis of polygonal rotating mirror 5 and reflecting surface is changed to 18.703mm respectively, 18.096mm, 18.096mm, 19.491mm, now, curvature of the image amount on sub scanning direction also changes, and is respectively 0.97mm, 0.11mm, 1.26mm.
At this, curvature of the image departs from paraxial foci position towards light beam direct of travel for+value expression paraxial converged position.As mentioned above, in order to obtain the balance of curvature of the image between image height, usually by the main sweep immediate vicinity of incident light beam strikes to polygonal rotating mirror reflecting surface, to obtain left-right balance, now, as shown in Figure 5, in periphery image height, the conjugate points s (1) of imaging surface one side is arranged in the front of surface to be scanned 8 (periphery image height is greater than the distance of the center of central image height from polygonal rotating mirror 5 to reflection spot from the distance of center to reflection spot of polygonal rotating mirror 5).If namely with light going direction be+, be in the other direction-, then s (1) is positioned at-direction.
To this, be in surface to be scanned to make conjugate points s (1), and the sweep trace reduced in periphery image height is unequal, need to make convergent point (the paraxial foci position namely on sub scanning direction) mobile from surface to be scanned 8 to light beam direct of travel (+direction).
Like this, when the sag of chain relative to central image height increases, can by making subscan curvature of the image relative to central image height to the change of+direction, it is unequal to reduce trace interval.Utilize such structure, such as, when the minute surface tilt quantity of polygonal rotating mirror 5 is 90s, trace interval is unequal is reduced to less than 5.8 μm.Now, significant image quality deterioration can not be felt during the eye observation image of people.
In addition, its scanning optics is preferably configured to by the light scanning apparatus 100 of present embodiment, image space sagging be generally the upper reflection of reflection position M (0) of 0 the chief ray of light beam and the optical axis of scanning optics be consistent.
And then because the sag of chain near central image height is minimum, and the sag of chain of periphery image height is maximum, and therefore, the subscan curvature of the image shape of preferred periphery image height is larger quadric surface.
The beam diameter degree of depth of central authorities' image height is greater than the beam diameter degree of depth of periphery image height usually, and for this reason, if secondary curvature of the image shape is in quadric surface shape, then, time on focal position imaging surface being coupled to periphery image height, the focus of central image height is easily given prominence to.That is, beam diameter deterioration can be avoided in whole image height and to improve trace interval unequal.
Moreover, as mentioned above, in order to obtain the sagging balance of image planes between image height, usually need the main sweep immediate vicinity of incident light beam strikes to polygonal rotating mirror minute surface, to obtain left-right balance, now, the distance between polygonal rotating mirror 5 center to reflection spot when the distance between polygonal rotating mirror 5 center to reflection spot when most cases is scanning beginning and the end of scan is roughly consistent.Like this, when the trace interval reducing periphery image height is unequal, the paraxial image planes position of periphery image height when scanning beginning and the end of scan is just consistent.Such structure can be avoided, in whole image height, beam diameter deterioration occurs, and improves trace interval unequal.
Fig. 7 A and Fig. 7 B shows the central image height of scanning optics and the depth curve of periphery image height on main scanning direction and sub scanning direction.Transverse axis in figure is the distance (defocusing (mm)) leaving imaging surface in the direction of the optical axis, and the longitudinal axis is the beam diameter (μm) of sub scanning direction.
In the imaging device 1000 carrying light scanning apparatus 100, define for the formation of the beam diameter size required for image, the degree of depth represented with L in Fig. 7 refers to the distance of the optical axis direction in the whole image height meeting the following condition of the non-prescribed level of beam diameter.
In addition, present embodiment is using the defocus amount of the beam diameter on beam waist position less than+10 μm as the degree of depth.As shown in Figure 7, usually, the degree of depth due to central image height is greater than the degree of depth of periphery image height, therefore the beam diameter on imaging surface that namely subscan curvature of the image mean in overstriking surface to be scanned is strengthened, but, if subscan curvature of the image is quadric surface, be then located at by imaging surface on the beam waist position of periphery image height, the beam diameter of central image height is because because the degree of depth is greatly and not easily thicker.In other words, can avoid, in whole image height, beam diameter deterioration occurs, improve trace interval unequal.
Moreover when strengthening subscan curvature of the image relative to central image height of periphery image height, do not wish that both depth curves intersect, the degree of depth of whole image height narrows.Usually, the degree of depth of central image height is greater than the degree of depth of periphery image height.For this reason, if make the depth curve of periphery image height be positioned at inside the depth curve of central image height, then the degree of depth of whole image height can be avoided to narrow.
In other words, the difference that the subscan curvature of the image of periphery image height can be allowed to be greater than the subscan curvature of the image of central image height is the value of the difference of the degree of depth of periphery image height and central image height.Such as, when the subscan curvature of the image amount of setting from imaging surface is β 1, β 2, β 3, and when the setting sub scanning direction degree of depth scanned in the middle of beginning, scanning, in scan end position is γ 1, γ 2, γ 3, two relational expressions establishments preferably.
&gamma; 2 - &gamma; 1 2 &le; &beta; 1 - &beta; 2 &le; &gamma; 2 - &gamma; 1
And
&gamma; 2 - &gamma; 3 2 &le; &beta; 3 - &beta; 2 &le; &gamma; 2 - &gamma; 3
If β 1-β 2 and β 3-β 2 is less than (γ 2-γ 1)/2, the effect that the trace interval that is then difficult to be improved is unequal, for this reason, in order to balanced scan distance between centers of tracks is unequal and beam diameter, the curvature of the image variation of preferred periphery image height is greater than (γ 2-γ 1)/2 relative to the image planes variation of central image height.
Such as, in the scanning optics (see embodiment 1) of present embodiment, relative to β 10.97mm, β 12=0.11mm, β 3=1.26mm, γ 1=14.5mm, γ 2=16mm, γ 3=14.5mm, all meets terms and conditions.
In addition, if strengthen the subscan curvature of the image of periphery image height, then in the image planes of whole image height, the degree of depth will reduce, and for this reason, the beam waist of preferred periphery image height is positioned at the imaging surface side (minus side) of previously shown paraxial image planes position.
Such as shown in Figure 7 B, paraxial foci position when image height is+161.5mm is+1mm, and now, beam waist position is positioned at-2mm.So, making the degree of depth of periphery image height symmetrical relative to imaging surface as much as possible, being conducive to being held in beam diameter in image planes to stablizing when there is product error.
Adopt the scanning optics of two panels above scan mirror 6 because of design parameter many, can consider to reduce the unequal method of trace interval when not causing and subscan curvature of the image deterioration (increase) occurring, but the less single lens optical system of design parameter to be difficult to reduce trace interval unequal, the scanning optics in therefore so far described light scanning apparatus 100 is particularly useful for the light scanning apparatus possessing single lens optical system.
Scan mirror 6 preferably adopts the plane of incidence and the surface of emission all to the bent moon eyeglass that light going direction protrudes.
When there is deflecting reflecting face 5a as shown in Figure 5 B in polygonal rotating mirror 5 and tilting, if the shape of the plane of incidence of scan mirror 6 is protruded towards light going direction, then the impact that brings of the variation of light angle is less, it is unequal that it can reduce trace interval further compared to biconvex shape, is conducive to image quality improving.
Above-mentioned scanning optics is especially effective to the light scanning apparatus (see Fig. 2) possessing multiple beam optical system.Fig. 8 shows the contrast table of the incident angle in aftermentioned embodiment 1 and comparative example 1 (single-beam optical system) in scanning optics in surface to be scanned 8.
When single beam mode, light beam can relative to surface to be scanned generally perpendicularly incident image planes, and when multiple beam mode, peripheral light beam is respectively to carry out incident respective image planes with vertical direction state at an angle.This represent polygonal rotating mirror 5 have minute surface tilt time, the amount of movement of the sub scanning direction that the imaging surface in multiple beam optical system occurs is more than what occur in single-beam optical system.Be specially, in comparative example 1, the incident angle of surface to be scanned 8 is 0 °, by contrast, maximum with the incident surface to be scanned 8 of the incident angle of 0.03 ° in the multiple beam optical system of embodiment 1.
In addition, above-mentioned embodiment is only be suitable for example of the invention process, does not form any limit value to the present invention, as long as the present invention can carry out various improvement without departing from the spirit and scope of the present invention.
< embodiment 1>
The embodiment of the scanning optics of light scanning apparatus of the present invention is below shown.The optical arrangement of the light scanning apparatus 100 of the present embodiment as shown in Figure 9.
Following formula represents the scan mirror shape etc. of embodiment 1.First, the non-radiused shape in main sweep cross section is represented with known polynomial expression (3).
X = Y 2 / R 1 + 1 - ( 1 + K ) ( Y / R ) 3 + A 1 Y + A 2 Y 2 + A 3 Y 3 + A 4 Y 4 + A 5 Y 5 + A 6 Y 6 + . . . . . . Formula (3)
At this, X is the degree of depth of this scanning mirror at optical axis direction, and R represents the paraxial radius-of-curvature in main sweep cross section, and Y represents the distance on main scanning direction and between optical axis, and K represents circular cone coefficient, and A1, A2, A3, A4, A5, A6 represent high power coefficient.
In above-mentioned formula (3), when coefficient A1, A3, A5 of odd number power are not equal to 0 but are more than 1, main scanning direction is asymmetrical shape.
When main scanning direction while being initial point (coordinate that Y represents with the optical axis position) curvature (inverse of radius-of-curvature) of being taken in subscan cross section changes, represent the curvature C (Y) in scanning mirror subscan cross section with following formula (4).
C ( Y ) = 1 r ( 0 ) + B 1 Y + B 2 Y 2 + B 3 Y 3 + B 4 Y 4 + B 5 Y 5 + B 6 Y 6 + . . . . . . Formula (4)
At this, r (0) represents the radius-of-curvature of this scan mirror in subscan cross section on optical axis, and B1, B2, B3 represent high power coefficient.
In above-mentioned formula (4) when the coefficient B 1 of the odd number power of Y, B3, B5 are not equal to 0 but be more than 1 time main scanning direction be asymmetrical shape, and when these coefficients are 0, scan mirror curvature is certain.
Be not limited to about special toric lens and represent with the formula of above-mentioned form, and available various formula represents.
The light source 1 of embodiment 1 is 4ch-LDA, and its wavelength is 655nm, be spaced apart 30 μm, light source rotational angle is 82.511 °.The focal length of coupling mirror 2 is 27mm, and this coupling mirror 2 is formed as parallel beam for the light beam launched by light source 1.The sub scanning direction focal length of cylindricality mirror 4 is 48mm.
Angle between the incident direction of the light beam that the deflecting reflecting face quantity of polygonal rotating mirror 5 is 6, inradius is 18mm, light source is launched and scanning optics optical axis is 68 °.
The data of the optical system of Figure 10 display between polygonal rotating mirror 5 and surface to be scanned 8.Wherein, R represents the radius-of-curvature of main scanning direction, and the radius-of-curvature of r vice direction of scanning, n represents refractive index.At this, R and r is paraxial radius-of-curvature.
X and Y in Figure 10 represent be numbered i ~ i+1 minute surface summit between at optical axis direction to remember the distance of direction of scanning.Such as, X=55.077 and Y=-0.892 being numbered 0 (deflecting reflecting face) represents, relative to deflecting reflection point position (giving the reflection position with image height 0), the summit of the plane of incidence (minute surface numbering 1) of scanning mirror 6 respectively at optical axis direction (X-direction) at a distance of 55.077mm, and at sub scanning direction (Y-direction) at a distance of-0.892mm.
The X=21.0 of minute surface numbering 1 represents the thickness of scanning mirror 6 on optical axis.The curvature of the plane of incidence (minute surface numbering i=1) is certain, and the shape in main sweep cross section is the non-radiused represented with above-mentioned formula (4).Figure 11 shows the main scanning direction of the plane of incidence and the coefficient of sub scanning direction.
The surface of emission (minute surface numbering i=2) is special, and the shape in its main sweep cross section is asymmetric circular arc relative to optical axis.Figure 12 shows the main scanning direction of the surface of emission and the coefficient of sub scanning direction.In the scanning optics of embodiment 1, horizontal magnification β=3.05 of the sub scanning direction of center image height.
Figure 13 A shows the curvature of the image characteristic of embodiment 1, and wherein realize vice scanning curvature of the image, the virtual image represents main sweep curvature of the image, and Figure 13 B shows uniform velocity characteristic (linear characteristic).In addition, the accompanying drawing after Figure 13 all shows in 4ch-LDA the optical characteristics of the ch1 being positioned at end.
Fig. 7 shows the depth curve (spot diameter with defocus change) of the spot diameter of each luminous point image height in embodiment 1, and it mainly refers to and is main sweep 65 ± 10 μm and the luminous point of subscan 80 ± 10 μm with the spot diameter of line spread function 1/e2 strength definition.
Scanning mirror 6 in the scanning optics of embodiment 1 adopts plastic material to be formed, but the present invention is not limited thereto, can also be formed with glass material.In addition, by making scanning optics eccentric, more preferably aberration compensation is carried out.In embodiment 1 by scanning mirror 6 relative to by the normal slope of scanning 8 0.25 degree, thus obtain good performance.
< comparative example 1>
Next illustrates a routine existing scanning optics (single-beam optical system, single lens optical system).At this, light source is single LD, its wavelength is 655nm, the focal length of coupling mirror is 15mm, the focal length of the sub scanning direction of cylindricality mirror is 48mm, the deflecting reflecting face quantity of polygonal rotating mirror is 6, and the inradius of this polygonal rotating mirror is 18mm, and the angle between the incident direction of the light beam that light source is launched and the optical axis of scanning optics is 68 °.
The data of the optical system of Figure 14 display between the polygonal rotating mirror and surface to be scanned of comparative example 1.Wherein, R represents the radius-of-curvature of main scanning direction, and the radius-of-curvature of r vice direction of scanning, n represents refractive index.At this, R and r is paraxial radius-of-curvature.X and Y in figure represent be numbered i ~ i+1 minute surface summit between at optical axis direction to remember the distance of direction of scanning.
The curvature of the plane of incidence (minute surface numbering i=1) is certain, and the shape in main sweep cross section is the non-radiused represented with above-mentioned formula (4).Figure 15 shows the main scanning direction of the plane of incidence and the coefficient of sub scanning direction.The surface of emission (minute surface numbering i=2) is special, and the shape in its main sweep cross section is asymmetric circular arc relative to optical axis.Figure 15 shows the main scanning direction of the surface of emission and the coefficient of sub scanning direction.In the scanning optics of comparative example 1, horizontal magnification β=3.73 of the sub scanning direction of center image height.
Figure 17 A shows the curvature of the image characteristic of comparative example 1, and wherein realize vice scanning curvature of the image, the virtual image represents main sweep curvature of the image, and Figure 17 B shows uniform velocity characteristic (linear characteristic).
Figure 18 shows the depth curve (spot diameter is with the change defocused) of the spot diameter of each luminous point image height in comparative example 1, and wherein, Figure 18 A is main scanning direction, and Figure 18 B is sub scanning direction.
Known with reference to Figure 17 and Figure 18, paraxial foci position and the beam waist position of the sub scanning direction of comparative example 1 are all about ± 1mm, and both are consistent.
Comparative example 1 and comparative example 1 known, the scanning mirror 6 of above-described embodiment 1 such as shown in Figure 7, all has the good degree of depth at main scanning direction and sub scanning direction, ° higher to the license of the positional precision of surface to be scanned 8.In addition, as shown in figure 13, the defocus positions of the periphery image height of embodiment 1 increases to "+" direction, successfully makes conjugate points close to surface to be scanned 8.Accordingly, validity of the present invention obtains confirmation.

Claims (10)

1. a light scanning apparatus, comprising: light source; First optical system, for light beam that described light source is launched on polygonal rotating mirror with line as imaging; And, second optical system, for by the light beam after the deflection of described polygonal rotating mirror on imaging surface with point as imaging, it is characterized in that, when the main scanning direction sub scanning direction carrying out deflection scanning with described polygonal rotating mirror is respectively first direction and second direction, and with simultaneously perpendicular to the direction of this first direction and this second direction for third direction time, this light scanning apparatus meets following relational expression:
α 2 < α 1, α 3 and β 2 < β 1, β 3, or,
α 2 > α 1, α 3 and β 2 > β 1, β 3,
Wherein, α 1, α 2, α 3 scanning be respectively when polygonal rotating mirror carries out deflection scanning starts, scan in the middle of, the end of scan time beam reflection position from the center of rotation of polygonal rotating mirror to polygonal rotating mirror distance, β 1, β 2, β 3 scanning be respectively when polygonal rotating mirror carries out deflection scanning starts, scan in the middle of, the end of scan time from imaging surface to described second direction light beam convergence paraxial foci position distance.
2. light scanning apparatus according to claim 1, is characterized in that, in this light scanning apparatus, following relational expression is set up,
&gamma; 2 - &gamma; 1 2 &le; &beta; 1 - &beta; 2 &le; &gamma; 2 - &gamma; 1
And,
&gamma; 2 - &gamma; 3 2 &le; &beta; 3 - &beta; 2 &le; &gamma; 2 - &gamma; 3
Wherein, the scanning that γ 1, γ 2, γ 3 are respectively described starts, scan in the middle of, the end of scan time described second direction the degree of depth.
3. light scanning apparatus according to claim 1, is characterized in that, this light scanning apparatus meets following relational expression,
α 2 < α 1, α 3 and β 2 < β 1, β 3.
4. light scanning apparatus according to claim 1, it is characterized in that, when with the light going direction of described third direction for positive dirction, and when being negative direction with opposite direction, described scanning start and the described end of scan time described second direction on paraxial foci position than described scanning in the middle of time described second direction on paraxial foci position be more positioned at positive dirction side.
5. light scanning apparatus according to claim 4, is characterized in that, the paraxial foci position in the described second direction when paraxial foci position in described second direction when described scanning starts and the described end of scan is consistent.
6. light scanning apparatus according to claim 1, is characterized in that, described second direction described scanning start and the end of scan time beam waist position than respective paraxial foci position more near imaging surface side.
7. light scanning apparatus according to claim 1, is characterized in that, described second optical system is formed with an optical element, and this optical element has energy on described first direction and described second direction.
8. light scanning apparatus according to claim 1, is characterized in that, at least has light source described in two or more.
9. light scanning apparatus according to claim 1, is characterized in that, described second optical system has meniscus shape, and this meniscus shape protrudes towards described light beam direct of travel in this second direction.
10. an imaging device, comprising multiple image carrier and light scanning apparatus, this light scanning apparatus scans with according to the light beam after the modulate image information on described multiple image carrier, it is characterized in that, this optical scanning device is set to the light scanning apparatus in claim 1 ~ 9 described in any one.
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