JP2010117556A - Method of adjusting optical scanning apparatus, and optical scanning apparatus adjusted by the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a method of adjusting an optical scanning apparatus by which a stable optical adjustment is performed, the optical performance of an apparatus is stabilized particularly while the apparatus is frequently used, and an optical scanning apparatus adjusted by the method. <P>SOLUTION: The optical scanning apparatus includes: a first optical system which condenses a luminous flux radiated from a semiconductor laser; an optical deflector which scanningly deflects the luminous flux; and a second optical system which images the scanningly deflected luminous flux onto a face to be scanned. The adjustment of each component is performed as follows: at least one of first and second optical systems has a diffraction optical element, the oscillation wavelength of the semiconductor laser immediately after the igniting the laser is denoted by λ1, and the wavelength of the semiconductor laser, which emits light on the whole image area in an actual operation state of the optical scanning apparatus, after the oscillation wavelength reaches a stable state is denoted by λ2, then the each member composing the optical scanning apparatus is optically adjusted at the wavelength λ3 which satisfies the condition (5λ1+λ2)/6<λ3<(λ1+λ2)/2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of adjusting an optical scanning device and an optical scanning device adjusted thereby, and optical scanning mounted on an image forming apparatus of a laser beam printer, a digital copying machine, or a multifunction printer (multifunction printer) having an electrophotographic process. It is suitable for the apparatus.

  Conventionally, an optical scanning device is used in a laser beam printer (LBP), a digital copying machine, a multifunction printer, or the like. In this optical scanning device, a light beam (light beam) that is light-modulated and emitted from a light source means in accordance with an image signal is periodically deflected by an optical deflector composed of, for example, a rotating polygon mirror (polygon mirror). The deflected light beam is focused in a spot shape on the surface of a photosensitive recording medium (photosensitive drum) by an imaging optical system having fθ characteristics, and image recording is performed by optically scanning the surface.

  FIG. 18 is a schematic view of a main part of a conventional optical scanning device.

  In the figure, a single or a plurality of divergent light beams emitted from the light source means 1 are converted into parallel light beams by a collimator lens 2, and the light beams are limited by a diaphragm 3, and a cylindrical lens 4 having a specific refractive power only in the sub-scanning direction. Is incident. Among the parallel light beams incident on the cylindrical lens 4, the light is emitted as it is in the main scanning section. In the sub-scan section, the light beam is focused and formed as a line image on the deflecting surface (reflecting surface) 5a of the optical deflector 5 comprising a polygon mirror.

  Then, the light beam deflected by the deflecting surface 5a of the optical deflector 5 is guided onto the photosensitive drum surface 8 as the surface to be scanned through the imaging lens 6 having the fθ characteristic. Then, by rotating the light deflector 5 in the direction of arrow A, image information is recorded by optically scanning the photosensitive drum surface 8 in the direction of arrow B (main scanning direction) with a single or a plurality of light beams. In FIG. 18, 18 is a synchronization detection mirror, and 19 is a synchronization detection sensor.

  Conventionally, various optical scanning apparatuses that perform temperature compensation using a diffractive optical element and adjustment methods thereof have been proposed (see Patent Documents 1 to 3).

  19A and 19B are cross-sectional views of main parts when the optical path of the optical scanning device disclosed in Patent Document 1 is developed. FIG. 19A is a main-scan cross-sectional view and FIG. B) is a sub-scan sectional view.

  In FIGS. 4A and 4B, the divergent light beam emitted from the light source means 1 is converted into a parallel light beam in the main scanning section and in the sub-scanning section by a single optical element 25 having anamorphic power (refractive power). Is converted into a focused light beam. The converted light beam is formed as a line image on the deflecting surface (reflecting surface) 5a of the optical deflector formed of a polygon mirror. A diffraction grating (elliptical grating) having anamorphic power is formed on the plane 201 on the light beam incident side of the optical element 25, and a surface 202 on the light beam emission side is a refracting surface having anamorphic power. ing.

  The main scanning sectional view in FIG. 6A shows a case where the polygon mirror is simplified and the center of the image is scanned. Actually, the polygon mirror composed of a large number of surfaces rotates, so that the light beam scans in the direction of arrow B, and the photosensitive drum (photosensitive drum surface) 8 rotates in the direction of arrow C shown in FIG. Thus, a two-dimensional image is drawn.

  In Patent Document 2, a long diffractive optical element is used in an image forming optical system for forming an image of a light beam deflected and scanned by a polygon mirror on a photosensitive drum surface as a scanned surface, and has excellent environmental stability. Optical scanning devices have been proposed.

  In the above Patent Documents 1 and 2, the aberration change accompanying the temperature change using the optical element (diffractive optical element) in which the diffraction grating is formed on the surface of the plastic lens, the power change of the refractive part and the diffractive part of the optical element, Correction is made based on the wavelength variation of the semiconductor laser.

Patent Document 3 proposes an adjustment method for correcting a difference in imaging point position based on a wavelength difference due to individual differences (manufacturing variation) of semiconductor lasers as light source means in an optical scanning device using the diffractive optical element. Has been.
JP 2006-154748 A JP 11-223783 A JP 2001-324691 A

  Conventionally proposed optical scanning devices using diffractive optical elements and adjustment methods thereof have the following problems.

  A semiconductor laser (also referred to simply as “laser”), which is generally used as a light source means of an optical scanning device, has mode hops caused by self-heating of the laser element itself and changes in ambient environmental temperature immediately after the laser is turned on. There is a so-called wavelength change. The amount of this wavelength change depends on the current value supplied to the semiconductor laser, the current flow time, etc., when the ambient environmental temperature is constant. The larger the current value, the larger the wavelength change amount. Even if the current value is constant, the wavelength change amount increases with the lighting time, and after a certain period of time, the wavelength changes when it reaches a thermally stable state. Stops.

  In addition, in order to make the rise of the emission waveform steep when pulse width modulation is performed, it is common to perform control with a bias current applied. This bias current warms the semiconductor laser element itself, and the amount of mode hops (wavelength change) tends to increase compared to light emission control in which no bias current flows.

  When the optical system from the light source means to the photosensitive drum surface, which is the surface to be scanned, is composed of at least one of a reflective optical element and a refractive optical element, optical performance deterioration such as focus shift due to wavelength change is a problem. There is no level. However, in an optical system using a diffractive optical element disclosed in Patent Documents 1 to 3 and the like, there is a great influence on optical performance with respect to wavelength change.

The Abbe number ν _d often used as an index indicating the intensity of dispersion of the optical material is ν _d = (n _d −1) / (n _F −n _C ) in the case of a refractive optical element.
A general optical material takes a value of 20 to 80.

On the other hand, the Abbe number ν _{d_diff in} the case of a diffractive optical element is defined by the following equation:
ν _d — _diff = λ _d / (λ _F −λ _C ) = 587.56 / (486.13−656.27) = − 3.453
It has a minus sign and exhibits a dispersion characteristic that is one order of magnitude stronger than that of a normal optical material in the visible range.

The partial dispersion ratio θ _{g, F} is θ _{g, F} = (λ _g −λ _F ) / (λ _F −λ _C ) = (435.84−486.13) / (486.13−656.27) = 0.2956
Thus, since ordinary optical materials are 0.53 to 0.63, it can be seen that they also have very large anomalous dispersion characteristics.

  As described above, even if the diffractive optical element has a very weak power, it has a strong dispersion characteristic as described above, so it must be used in consideration of performance degradation with respect to wavelength change.

  The adjustment method shown in Patent Document 3 corrects a difference in imaging point position based on a wavelength difference due to individual differences (manufacturing variation) of semiconductor lasers as light source means in an optical scanning device using a diffractive optical element. It is adjustment. Patent Document 3 is not an adjustment method that takes into account the shift of the imaging point position due to the wavelength change caused by the mode hop of the semiconductor laser described above.

  Therefore, in various optical scanning devices using the adjustment method that has been conventionally used, there is a problem in density stability particularly in the halftone region.

  Further, if the optical adjustment is performed in a state where the wavelength is changed, the adjustment itself depends on the elapsed time from the start of lighting of the semiconductor laser, so that there is a problem that stable optical adjustment cannot be performed.

  The present invention provides an optical scanning device adjustment method capable of performing stable optical adjustment and stabilizing the optical performance of the device, particularly in a state in which the device main body is frequently used, and an optical scanning device adjusted thereby. Objective.

The adjustment method of the optical scanning device of the invention of claim 1
A semiconductor laser, a first optical system for condensing a light beam emitted from the semiconductor laser, an optical deflector for deflecting and scanning the light beam from the first optical system, and deflected and scanned by the optical deflector In an adjustment method of an optical scanning device for adjusting each member constituting an optical scanning device having a second optical system that forms an image of a light beam on a surface to be scanned,
At least one of the first optical system and the second optical system has a diffractive optical element,
The oscillation wavelength immediately after turning on the semiconductor laser is λ1,
When the semiconductor laser is caused to emit light in the entire image region in the actual use state of the optical scanning device, and the wavelength after the oscillation wavelength of the light beam emitted from the semiconductor laser is stabilized is λ2,
(5λ1 + λ2) / 6 <λ3 <(λ1 + λ2) / 2
Each member constituting the optical scanning device is optically adjusted at a wavelength of λ3 that satisfies the following conditions.

The invention of claim 2 is the invention of claim 1,
At the time of the optical adjustment, a laser beam having an oscillation wavelength λ1 oscillated by the semiconductor laser is performed, and then an optical adjustment value adjusted by a light beam having a wavelength λ1 is used.
(Λ2-λ1) / 6 <Δλ <(λ2-λ1) / 2
The optical adjustment is performed again so that the optical adjustment value is shifted by an amount corresponding to the wavelength difference Δλ that satisfies the above condition.

The invention of claim 3 is the invention of claim 1 or 2, wherein
The first optical system includes a diffractive optical element, and in the optical adjustment, focus adjustment is performed by displacing a position of the optical element included in the first optical system or a position of the semiconductor laser. Yes.

The invention of claim 4 is the invention of any one of claims 1 to 3,
The second optical system includes a diffractive optical element, and in the optical adjustment, the optical deflector is displaced by displacing a position of an optical element included in the second optical system or a mounting position of the optical scanning device. The conjugate relationship between the deflection surface and the scanned surface is adjusted.

The invention of claim 5 is the invention of any one of claims 1 to 4,
At the time of the optical adjustment, the emission duty of the semiconductor laser is set to 20% or less.

An adjustment method for an optical scanning device according to a sixth aspect of the present invention comprises:
A light beam oscillated from a semiconductor laser is condensed by a first optical system, the condensed light beam is deflected and scanned by an optical deflector, and the deflected and scanned light beam is scanned via a second optical system. In the adjustment method of the optical scanning device for adjusting each member constituting the optical scanning device that forms an image on the surface,
During the optical adjustment, the emission duty of the semiconductor laser is set to 20% or less.

The invention of claim 7 is the invention of any one of claims 1 to 6,
The semiconductor laser is fixed to a holder made of resin.

An adjustment method of the optical scanning device according to the invention of claim 8 comprises:
A semiconductor laser, a first optical system for condensing a light beam oscillated from the semiconductor laser, an optical deflector for deflecting and scanning the light beam from the first optical system, and a light beam deflected and scanned by the optical deflector And a second optical system that forms an image on the surface to be scanned,
At least one of the first optical system or the second optical system has a diffractive optical element,
The depth center position in the main scanning direction at the center of the image immediately after the semiconductor laser is turned on is Xm1, and the depth center position in the sub-scanning direction is Xs1,
In the actual use state of the optical scanning device, the semiconductor laser is oscillated all over the image area, and the depth center position in the main scanning direction at the image center after the oscillation wavelength is stabilized is Xm2, and the depth center position in the sub-scanning direction Is Xs2 and the scanned surface position is Xt.
(Xm1 + Xm2) / 2 <Xt <(5Xm1 + Xm2) / 6
Or
(Xs1 + Xs2) / 2 <Xt <(5Xs1 + Xs2) / 6
It is characterized by satisfying at least one of the following formulas.

The invention of claim 9 is the invention of claim 8,
The semiconductor laser is fixed to a holder made of resin.

An image forming apparatus according to the invention of claim 10
An optical scanning device adjusted by the optical scanning device adjustment method according to claim 1 or an optical scanning device according to claim 8 or 9, and a photoconductor disposed on the surface to be scanned. A developing unit that develops an electrostatic latent image formed on the photosensitive member by a light beam scanned by the optical scanning device as a toner image, and a transfer unit that transfers the developed toner image to a transfer material. And a fixing device for fixing the transferred toner image to the transfer material.

The invention of claim 11 is the invention of claim 10,
A printer controller for converting a signal input from an external device into image data is provided.

  According to the present invention, there is provided an optical scanning device adjustment method capable of performing stable optical adjustment and stabilizing the optical performance of the device particularly when the device main body is frequently used, and an optical scanning device adjusted thereby. Can be achieved.

  An adjustment method of an optical scanning device of the present invention includes a semiconductor laser, a first optical system that collects a light beam emitted from the semiconductor laser, an optical deflector that deflects and scans a light beam from the first optical system, Each member of the second optical system that focuses the light beam deflected and scanned by the optical deflector on the surface to be scanned is adjusted.

  At least one of the first optical system and the second optical system has a diffractive optical element, and at the time of optical adjustment, the optical adjustment of each member constituting the optical scanning device is performed at the target wavelength λ3. Made.

  Here, the wavelength λ3 is a wavelength considering the wavelength λ1 immediately after the semiconductor laser is turned on and the wavelength λ2 when the oscillation wavelength is stabilized.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a sectional view (main scanning sectional view) of the main part in the main scanning direction according to the first embodiment of the present invention.

  In the following description, the expression “on the optical axis or on the axis of the imaging optical system” means an axis perpendicular to the scanned surface at the center of the scanned surface. When expressed as the optical axis of the lens, it means a straight line connecting the surface vertices of the entrance surface and the exit surface of the lens.

  The sub-scanning direction (Z direction) is a direction parallel to the rotation axis of the deflecting unit. The main scanning section is a section whose normal is the sub-scanning direction (direction parallel to the rotation axis of the deflecting means). The main scanning direction (Y direction) is the direction in which the light beam deflected and scanned by the deflecting means is projected onto the main scanning section. The sub-scanning cross section is a cross section whose normal is the main scanning direction.

  In FIG. 1, reference numeral 1A denotes a light source means (light source), which is composed of, for example, a semiconductor laser. In this embodiment, an infrared semiconductor laser having a design wavelength of 790 nm is used. Reference numeral 3A denotes an aperture that restricts the luminous flux (light quantity).

  Reference numeral 2A denotes an optical element having anamorphic power as a first optical system. The light beam emitted from the light source means 1A is converged in the main scanning section in the parallel scanning section and in the sub-scanning section to be converged. A line image is formed on the deflection surface 5a.

  The optical element 2A in the present embodiment has an anamorphic lens in which the incident surface of the light beam is formed of a diffraction grating (elliptical grating) having an anamorphic power on a flat surface, and the radiating surface of the light beam is formed of an anamorphic refractive surface. (Also referred to as a diffractive optical element).

  Each element of the aperture stop 3A and the anamorphic lens 2A constitutes an element of the incident optical system (condensing optical system) LA.

  In the present embodiment, the first optical system is configured by an anamorphic lens. However, the present invention is not limited to this. For example, a collimator lens or a cylindrical lens may be used. In this case, a diffraction grating having anamorphic power may be provided on at least one surface of the collimator lens or the cylindrical lens.

  An optical deflector (polygon mirror) 5 as a deflecting means has a five-surface configuration with a circumscribed circle radius of 17 mm. Further, the polygon mirror 5 is rotated at a constant speed in the direction of arrow A shown in the figure by a motor (not shown), thereby scanning the surface to be scanned 8A in the direction of arrow B (main scanning direction).

  SA is an imaging optical system as a second optical system, and includes first and second imaging lenses (fθ lenses) 6A and 7A. The imaging optical system SA forms an image of a light beam based on the image information deflected and scanned by the optical deflector 5 on the photosensitive drum surface 8A as a surface to be scanned. In addition, the imaging optical system SA performs surface tilt compensation of the deflection surface 5a by making a conjugate relationship between the deflection surface 5a of the optical deflector 5 and the photosensitive drum surface 8A in the sub-scan section.

  Usually, in the case of an optical deflector having a plurality of deflecting surfaces such as a polygon mirror, the tilting angle of the deflecting surface in the sub-scanning direction is different for each deflecting surface. is there.

  In this embodiment, the imaging optical system SA is composed of two lenses. However, the present invention is not limited to this. For example, the imaging optical system SA may be composed of a single lens or three or more lenses.

  Reference numeral 8A denotes a photosensitive drum surface as a surface to be scanned.

  In this embodiment, the divergent light beam emitted from the semiconductor laser 1A as the light source means is limited in light quantity by the aperture 3A and enters the anamorphic lens 2A. Out of the light beam incident on the anamorphic lens 2A, the light beam is emitted as it is in the main scanning section. In the sub-scan section, the light beam converges and forms a line image (a line image long in the main scanning direction) on the deflecting surface 5a of the optical deflector 5.

  The light beam deflected and scanned by the deflecting surface 5a of the optical deflector 5 is spot-formed on the photosensitive drum surface 8A by the imaging optical system SA, and the photosensitive deflector 5 is rotated in the direction of arrow A by rotating the optical deflector 5 in the direction of arrow A. Optical scanning is performed on the surface 8A in the arrow B direction (main scanning direction) at a constant speed. As a result, a single scanning line or a plurality of scanning lines are simultaneously formed on the photosensitive drum surface 8A, which is a recording medium, to perform image recording.

  FIG. 2 is a sectional view (sub-scanning sectional view) of the principal part in the sub-scanning direction when the optical scanning device of the present invention shown in FIG. 1 is used in a color image forming apparatus. In the figure, the same elements as those shown in FIG.

  The color image forming apparatus in the figure includes two scanning units SR and SL with the deflecting means 5 interposed therebetween. Then, the four light beams Ra, Rb, R′a, R′b are deflected and scanned by one deflecting means 5, and the corresponding photosensitive drum surfaces 8A (Bk), 8B (C), 8C (M), 8D ( Y) is being scanned.

  Here, in the scanning unit SR, the deflected light beam Ra deflected and reflected by the deflecting surface 5a of the optical deflector (five-sided polygon mirror) 5 serving as a deflecting means passes through the imaging lenses 6A and 7A and is then folded by the reflecting mirror M1. Then, it is guided to the photosensitive drum 8A (Bk) which is the surface to be scanned. Further, the deflected light beam Rb deflected and reflected by the deflecting surface 5a of the optical deflector 5 passes through the imaging lens 6A, is then folded by the reflecting mirrors M2 and M3, passes through the imaging lens 7B, and is folded by the reflecting mirror M4. Then, it is guided to the photosensitive drum 8B (C) which is the surface to be scanned.

  On the other hand, in the scanning unit SL, the deflected light beam R′a deflected and reflected by the deflecting surface 5′a of the optical deflector 5 passes through the imaging lenses 6′A and 7′A, and is then folded by the reflecting mirror M′1. It is guided to the photosensitive drum 8D (Y) that is the surface to be scanned. Further, the deflected light beam R′b deflected and reflected by the deflecting surface 5′a of the optical deflector 5 passes through the imaging lens 6′A and is then folded back by the reflecting mirrors M′2 and M′3 to pass through the imaging lens 7′B. Then, the light is returned by the reflecting mirror M′4 and guided to the photosensitive drum 8C (M) which is the surface to be scanned.

  In the figure, C0 is the deflection point of the principal ray of the axial light beam. In the sub-scanning direction, the light beams Ra and Rb (R′a and R′b) intersect at the deflection point C0. The deflection point C0 is a reference point of the imaging optical system, and the distance from the deflection point C0 to the scanned surface is hereinafter defined as “optical path length of the imaging optical system”.

  In this embodiment, the light beams emitted from the plurality of light source means are incident on the different deflection surfaces of one optical deflector through the corresponding incident optical systems, and both sides sandwiching the optical deflector are arranged. Deflection scanning. This achieves an optical scanning device that can simultaneously scan four colors of yellow (Y), magenta (M), cyan (C), and black (Bk).

  In FIG. 2, 9 is a motor, 10 is an optical box (housing), and 11 is an optical scanning device.

  FIG. 3 is a cross-sectional view of a main part of the sub-scan of the incident optical systems LA and LB of one scanning unit SR in the color image forming apparatus shown in FIG. In the figure, the same elements as those shown in FIG.

  The incident optical system of the other scanning unit SL has the same configuration and optical action as the incident optical system of the scanning unit SR.

  In this embodiment, an infrared semiconductor laser (design wavelength: 790 nm) 1A, 1B is used as a light source means, and divergent light beams emitted from the infrared semiconductor lasers 1A, 1B are anamorphic having an anamorphic power through the apertures 3A, 3B. The light is incident on the lenses 2A and 2B. Then, from the anamorphic lenses 2A and 2B, the parallel light beam is focused in the main scanning section, and the light beam is focused in the sub-scanning section and focused as a line image on the deflecting surface (reflecting surface) 5a of the optical deflector 5 composed of a polygon mirror. Yes.

  In the anamorphic lenses 2A and 2B, as described above, the light incident surfaces 201A and 201B have a diffraction grating (ellipsoidal grating) having anamorphic power on the plane, and the light emitting surfaces 202A and 202B have anamorphic refraction. It is formed with a surface.

  In this embodiment, the anamorphic lenses 2A and 2B are integrated by plastic molding to produce a two-lens anamorphic lens 20.

The apertures 3A and 3B limit the beam width so that a desired spot diameter (1 / e ² slice diameter of the spot peak light amount) can be obtained on each scanned surface.

  In this way, the actions of the collimator lens and the cylindrical lens are integrated into the anamorphic lenses 2A and 2B having anamorphic power, and the anamorphic lenses 2A and 2B are integrated vertically to reduce the number of parts and simplify the entire apparatus. I am trying.

  In this embodiment, when a plane perpendicular to the deflection surface 5a of the optical deflector 5 and passing through the reference point C0 is P0, γa = 3.0 ° and γb = 3.0 with respect to the plane P0, respectively. A light beam having an oblique incident angle of ° is deflected and scanned.

  In FIG. 3, reference numeral 12 denotes a laser unit, LA denotes an incident optical system on the infrared semiconductor laser 1A side, and LB denotes an incident optical system on the infrared semiconductor laser 1B side.

Next, Table 1 shows the lens surface shape and optical arrangement of the optical scanning device according to this embodiment. Table 1 shows the surface shape of the imaging optical system that passes the light beam Ra and the optical arrangement when the optical path is developed. Since the light beams Rb, R′a, and R′b are the same as the optical system for Ra, specific numerical values such as the lens surface shape are omitted. Note that the display of “ ^EX ” means “× 10 ^−X ”.

  Here, Table 1 shows lens shapes and arrangements of the imaging optical system SA and the incident optical system LA.

  The generatrix shapes of the lens entrance surfaces and lens exit surfaces of the imaging lenses (fθ lenses) 6A and 7A are aspherical shapes that can be expressed as functions up to the 10th order. The intersection between the lens surfaces of the imaging lenses 6A and 7A and the optical axes of the imaging lenses 6A and 7A is the origin, the optical axis direction is the X axis, and the axis orthogonal to the optical axis in the main scanning section is the Y axis. To do. At that time, the bus direction corresponding to the main scanning direction is

(Where R is the radius of curvature of the bus, and K, B ₄ , B ₆ , B ₈ , B ₁₀ are aspherical coefficients)
It is expressed by the following formula.

The aspheric coefficients B ₄ , B ₆ , B ₈ , and B ₁₀ are arranged on the side (B _4s , B _{6 s} , B _{8 s} , B _{10 s} ) on which the semiconductor laser 1A of the optical scanning device is arranged and the semiconductor laser 1A. The numerical values are different from those on the side that is not (B _4e , B _{6 e} , B _{8 e} , B _{10 e} ). As a result, an asymmetric shape in the main scanning direction can be expressed.

  Also, the direction of the child line corresponding to the sub-scanning direction is

It is expressed by the following formula. S is a child line shape defined in a plane perpendicular to the main scanning plane including the normal line of the bus bar at each position in the bus bar direction.

  Here, the radius of curvature (sub-wire curvature radius) Rs * in the sub-scanning direction at a position Y away from the optical axis in the main scanning direction is

(However, Rs is the radius of curvature of the strand on the optical axis, and D ₂ , D ₄ , D ₆ , D ₈ , and D ₁₀ are the strand changing coefficients)
It is expressed by the following formula.

This is also performed in the same manner as the shape in the main scanning direction. That is, the aspheric coefficients D ₂ , D ₄ , D ₆ , D ₈ , and D ₁₀ are arranged on the side (D _2s , D _4s , D _6s , D _8s , D _10s ) on which the semiconductor laser 1A of the optical scanning device is arranged. _Different values are used on the side that is not (D _2e , D _4e , D _6e , D _8e , D _10e ). As a result, an asymmetric shape in the main scanning direction can be expressed.

  The surface 201A on the light beam incident side of the anamorphic lens 2A is a diffraction grating surface defined by the following phase polynomial.

_{φ = 2πm / λ0 {C 1} Z + C 2 Y + C 3 Z 2 + C 4 ZY + C 5 Y 2 ···}
φ is the phase function, m is the diffraction order, and λ 0 is the reference wavelength. In this embodiment, 790 (nm), m is the diffraction order, and in this embodiment, the first order is used.

  The exit surface 202A is a toric surface having a radius of curvature Rm in the main scanning direction of Rm = -27.8387 and a radius of curvature Rs in the sub-scanning direction of Rs = -20.3713.

  In the present embodiment, the function of the surface shape is defined by the above definition formula, but the scope of the right of the present invention is not limited thereto.

  If the power of the diffraction grating is determined as described above, the entire optical scanning device (incident optical element, scanning luminous element, and semiconductor laser) is compensated for defocus when the temperature rises uniformly (temperature compensation effect). ).

The temperature characteristic of the wavelength of the semiconductor laser is
dλ / dt = 0.255 nm / ° C.
The temperature characteristic of the refractive index of plastic material is
dn / dt = −7.896E−5 / ° C.,
The wavelength characteristic of the refractive index of plastic material is
dn / dλ = −2.290E−5 / ° C.
The focus shift when the temperature is raised by 20 ° C. using these is calculated as follows.

Main scanning direction dm = + 0.39
Sub-scanning direction ds = −0.41
In this embodiment, the imaging lens 7A is rotated by 0.2 minutes clockwise from the optical deflector side with the optical axis as the rotation axis. The imaging lens 7B is rotated by 0.2 minutes counterclockwise as viewed from the optical deflector side with the optical axis as the rotation axis. In this way, the inclination of the scanning line is corrected.

  In general, in an optical scanning device in which a light beam is incident from an oblique direction in a sub-scanning section, a phenomenon that a spot is broken due to twist of wavefront aberration is observed.

  In this embodiment, the twist of wavefront aberration is reduced by optimizing the power arrangement of each surface, the tilt amount of the lens, and the shift amount. In the imaging optical system SA, the wavefront aberration is corrected by shifting the imaging lens 7A in the sub-scanning direction of 1.50 mm with respect to the surface P0.

  Here, the emission duty of the semiconductor laser used in the following description will be described with reference to FIG. FIG. 20 is a diagram in which a diagram of an optical scanning device is shown together with a laser emission sequence.

  In FIG. 20, Ta is a light emission time for laser light amount adjustment (auto power control) performed for each scanning line before writing an image. Tb is a light emission time for synchronization detection performed to align the writing position of the image in the main scanning direction. Tc is a light emission time for performing an effective image area to actually write an image. Td is the time that can be deflected and scanned by one surface of the polygon mirror, and is the same as the time required to rotate 72 ° for a five-surface polygon. The time Td is the same time as the synchronization detection period Te.

Using these times to define the laser emission duty, when the entire effective image area is lit,
Luminescence Duty = (Ta + Tb + Tc) / Td × 100 (%)
It becomes.

The emission duty when a part (α%) of the effective image area is emitted is
Luminescence Duty = (Ta + Tb + Tc × α / 100) / Td × 100 (%)
It becomes.

  FIG. 4 is a graph showing the wavelength change after the light emission when one semiconductor laser emits light using the lighting circuit of the semiconductor laser used in the optical adjustment in this embodiment.

  Laser lighting is the result of measuring PWM emission (pulse width modulation) at a frequency of 50 kHz and measuring the emission duty at two of 10% and 61.2%. Further, in this lighting circuit, no bias current is passed to suppress self-heating of the laser element as much as possible. In a low emission duty such as 10% duty, there is little heat accumulation and no wavelength change due to mode hop is observed. However, in the case of Duty 61.2%, the wavelength changes to the long wavelength side by about 0.8 nm after about 2 minutes due to two mode hops.

  In order to perform stable optical adjustment and improve the reproducibility of measurement, it is necessary to turn on the light emission mode so as not to change the wavelength. In order to do so, a low light emission duty with a light emission duty of 20% or less is preferable.

  Furthermore, considering the difference in the structure of the laser elements, manufacturing variations, etc., for example, it is desirable to emit light with a duty of 10% or less by PWM modulation at 50 kHz without passing a bias current. Hereinafter, this light emission mode is defined as “light emission mode 1”.

  On the other hand, the same semiconductor laser as that measured in FIG. 4 is turned on in the actual use state of the optical scanning device, and the wavelength change is measured in FIG.

  In the actual use state of the optical scanning device in the present embodiment, since the five-sided polygon mirror rotates at 38267.7 rpm, synchronization detection is performed at an interval of 313.58 μs (3.189 kHz). The scanable angle of the five-sided polygon mirror is 360/5 × 2 = 144 °, and the scanning angle of view of the optical scanning device of this embodiment is 83.49 °. Therefore, even if the entire image area is turned on, The light emission time is 58.0%. In addition, when combined with the light emission for APC (auto power control) and synchronization detection (BD), the maximum light emission time is 61.2%. Therefore, since the maximum value is 61.2%, it is not necessary to consider the wavelength change when light is emitted at a duty of 61.2% or more.

  Further, in the actual use state of the optical scanning device, control with a bias current is performed in order to make the emission waveform rise sharply when pulse width modulation is performed. Due to this bias current, even if the laser element itself warms up and emits light only for APC and synchronous detection (Duty approx. 3%), about 3 nm after about 3 minutes due to three mode hops, the long wavelength side The wavelength will change.

  In the actual use state of the product, the oscillation wavelength immediately after the semiconductor laser is turned on is λ1 (λ1 = 793.4 nm in FIG. 5). In addition, the maximum emission time in the actual use state of the product (image 100% + APC + synchronous detection) (Duty 61.2%) (all in the image area in the actual use state) and the oscillation wavelength of the light beam emitted from the semiconductor laser The wavelength after the stabilization is λ2 (λ2 = 795.76 nm in FIG. 5).

  In addition, the wavelength sensitivity of the focus of this optical scanning device (the amount of change in focus position when the wavelength changes by 1 nm) is -0.71 mm / nm in the main scanning direction and -1.27 mm / nm in the sub-scanning direction. ing.

  Therefore, in the actual use state of the product, the wavelength difference is λ2−λ1 = 2.36 nm from the state after the image of 100% density has been taken out for almost 10 minutes immediately after lighting, and in the main scanning direction in terms of focus. Deviation of −1.67 mm and −3.00 mm occurs in the sub-scanning direction. This is not a negligible amount considering the design depth.

  Further, in the region S surrounded by the dotted line and the region M surrounded by the solid line in FIG. 5, there are many opportunities for printing in the region S, and the optical performance in the region S is particularly important. Therefore, the adjustment with an emphasis on the region S may be performed by optical adjustment on the shorter wavelength side than (λ1 + λ2) / 2 rather than the adjustment at the wavelength (λ1 + λ2) / 2 which is exactly between the wavelengths λ1 and λ2.

  Further, if the adjustment is made with the wavelength λ1 itself immediately after the start of lighting, the region M cannot be covered and the adjustment is unbalanced.

Therefore, it can be said that determining the adjustment value in the wavelength region indicated by the following conditional expression (1) is a preferable adjustment method in consideration of actual use of the product. That means
(5λ1 + λ2) / 6 <λ3 <(λ1 + λ2) / 2 (1)
It is desirable to perform optical adjustment of each member constituting the optical scanning device at a wavelength of wavelength λ3 that satisfies the following conditions.

In the case of this example,
793.8 nm <λ3 <794.6 nm (1a)
It is desirable to determine the adjustment value in the wavelength region.

  The wavelength at which the optical adjustment is performed is related to the specifications of the image forming apparatus main body. In a high-speed machine that outputs 30 sheets or more per minute, there is an opportunity to output a large amount, so it is preferable to adjust near the upper limit value of the conditional expression (1).

  On the other hand, a low-speed machine with 20 or less output sheets rarely outputs a large amount, so it is preferable to adjust near the lower limit value of the conditional expression (1).

  In this embodiment, it is only necessary that the adjustment value of the optical scanning device finally optically adjusted be determined within the wavelength range of the conditional expression (1), and which wavelength is actually used for the adjustment. It doesn't matter.

  The adjustment may be actually performed at a wavelength within the range of the conditional expression (1), or the adjustment value may be shifted after adjustment is performed at a wavelength outside the range of the conditional expression (1). .

  However, when adjusting at a wavelength within the range of the conditional expression (1), there are problems described below, so the method of shifting the adjustment value after adjusting at a stable wavelength is simpler and more stable. It's a method.

  In order to set the wavelength of the semiconductor laser to, for example, near λ3 = 794.2 nm, when a semiconductor laser lighting circuit used for optical adjustment is used, it takes about 2 minutes at a duty of 61.2%, and the adjustment time becomes longer accordingly. End up. In addition, if the semiconductor laser is intentionally warmed to reach the wavelength 794.2 nm quickly, it becomes difficult to stabilize the wavelength thereafter.

  Therefore, since the wavelength of the above-described emission mode 1 is stable immediately after the start of laser lighting, the actual optical adjustment is performed by turning on the light at the wavelength λ1. Then, the amount of focus movement corresponding to Δλ = λ3−λ1 may be obtained in advance, and the optical adjustment value may be offset so as to satisfy the following conditional expression (2).

That is, at the time of optical adjustment, it is performed with a laser beam having an oscillation wavelength λ1 oscillated by a semiconductor laser, and thereafter, with respect to an optical adjustment value adjusted with a light beam having a wavelength λ1,
(Λ2-λ1) / 6 <Δλ <(λ2-λ1) / 2 (2)
The optical adjustment may be performed again so that the optical adjustment value is shifted by an amount corresponding to the wavelength difference Δλ that satisfies the above condition.

  If the conditional expression (2) is satisfied, the wavelength does not change and stable optical adjustment can be performed quickly, and at the same time, the optical adjustment is performed at the target wavelength (wavelength satisfying the conditional expression (1)) λ3. The same optical performance can be obtained.

  This embodiment is particularly effective when the semiconductor laser is fixed to a holder made of resin.

  Since the resin holder is inferior in heat dissipation to a metal holder or the like, a large wavelength change as shown in FIGS. 4 and 5 occurs. Therefore, the present embodiment works effectively for a resin holder that lacks stability in optical performance.

  What has been described above is described below with respect to the depth center position of the optical scanning device.

Here, when the depth center is plotted on the graph with the spot diameter on the vertical axis and the position in the optical axis direction on the horizontal axis (see FIG. 21), a slice level with a spot diameter (for example, 1.25 of the minimum spot diameter Dmin). Defined as the center of the position in the optical axis direction across The spot diameter is defined as a diameter sliced at 1 / e ² of the spot peak light quantity.

  FIG. 6 is a diagram for explaining the relationship between the depth center position and the surface to be scanned at each wavelength according to the first embodiment of the present invention.

In the figure, the depth center position in the main scanning direction at the image center immediately after the semiconductor laser is turned on (wavelength is λ1) is Xm1, and the depth center position in the sub-scanning direction is Xs1 (not shown). Furthermore, after the semiconductor laser is oscillated in the entire image area in the actual use state of the optical scanning device and the oscillation wavelength is stabilized (wavelength is λ2), the depth center position in the main scanning direction at the image center is Xm2, sub-scanning The depth center position in the direction is Xs2 (not shown), and the surface to be scanned is Xt. then,
(Xm1 + Xm2) / 2 <Xt <(5Xm1 + Xm2) / 6 (3)
Or
(Xs1 + Xs2) / 2 <Xt <(5Xs1 + Xs2) / 6 (4)
It is desirable to set the scanned surface position Xt so as to satisfy at least one of the following conditions.

  FIGS. 7A and 7B are cross-sectional views of the main part of the optical system of the adjusting tool used for adjusting the semiconductor laser of this embodiment. FIG. 4A is a sub-scanning sectional view, and FIG. 4B is a main-scanning sectional view. In FIGS. 4A and 4B, the same elements as those shown in FIG.

  In FIGS. 2A and 2B, the semiconductor laser 1A side is adjusted, but the semiconductor laser 1B is also adjusted with the adjustment tool 50 having the same configuration. In this embodiment, adjustments are made regarding the irradiation position (imaging position) and focus position of the incident optical system LA.

  In the present embodiment, a light beam emitted from the anamorphic lens 20 is a jig cylinder lens 51 (focal length 120 mm) having power only in the sub-scanning direction, and a jig spherical lens 52 (focal length 200 mm) composed of two bonded lenses. Pass through. The passing light beam is imaged in a spot shape at the adjustment target position T0.

  As shown in FIGS. 2A and 2B, it is important that the optical system of the adjustment tools 51 and 52 is composed of a plurality of lenses having different Abbe numbers and corrects longitudinal chromatic aberration. If the axial chromatic aberration is not corrected, it is impossible to distinguish between the axial chromatic aberration generated in the anamorphic lens 20 and the axial chromatic aberration generated in the optical system on the adjustment tool side.

  The aerial image formed at the adjustment target position T0 is measured by the objective lens 53 with an area sensor composed of a two-dimensional CCD. In the figure, reference numeral 54 denotes a laser light emission circuit for adjustment.

  FIG. 8 is a flowchart of optical adjustment of the optical scanning device in this embodiment.

  In this embodiment, since the anamorphic lenses 2A and 2B are integrally formed by plastic molding, the optical member displaced by optical adjustment is a semiconductor laser. Finally, the optically adjusted semiconductor lasers 1A and 1B and the anamorphic lens 20 are fixed to a holder (not shown) to complete the laser unit 12.

  First, the anamorphic lens 20 is fixed to the holder with an ultraviolet curable adhesive or the like (step 1). Next, the anamorphic lens 20 is attached to the adjustment tool through the holder (step 2), and the laser is operated in the stable light emission mode (light emission mode 1: no bias current, 50 kHz PWM light emission, Duty 10%) that does not cause the wavelength change described above. Is turned on (step 3). In the optical adjustment, the semiconductor laser 1A is first moved in the Y direction and the Z direction, and the irradiation position is adjusted so as to coincide with the adjustment target position T0 (step 4).

  Next, the semiconductor laser 1A is moved in the optical axis direction (X direction) to adjust the focus position (step 5). In this state, since the focus position is adjusted to be the best at the wavelength λ1, the adjustment value is shifted in the next step 6.

  In this embodiment, Δλ = 0.8 nm, and the corresponding position of the semiconductor laser 1A is 12 μm. Therefore, the semiconductor laser 1A is uniformly moved by 12 μm in the direction approaching the anamorphic lens 20 from the state adjusted to the focus best at the wavelength λ1. This is the same state as when optical adjustment is actually performed with a light beam having a target wavelength (wavelength satisfying conditional expression (1)) λ3, and in this state, the semiconductor laser 1A is bonded and fixed to the holder (step 7). ).

  After the above adjustment is completed, the laser unit 12 is removed from the adjustment tool 50 (step 8) and fixed to the optical box (housing) 10 in the assembly step of the scanner unit 11 (step 9).

  Here, as another method of Step 6, instead of bringing the semiconductor laser 1A closer to the 12 μm uniform anamorphic lens 20, the target position T0 corresponding to Δλ = 0.8 nm is shifted in a direction away from the anamorphic lens 20 at a position T0 ′. Do as. Even if it carries out like this, it is the same as the method of the said process 6. FIG.

In this example,
T0 '= T0 + 0.53
It becomes. In this way, it does not take time to move the 12 μm laser uniformly, and sudden (stable) optical adjustment can be performed.

  The adjustment method on the semiconductor laser 1B side is the same as the adjustment method described above.

  In this embodiment, the adjustment is performed by displacing the position of the semiconductor laser. However, when there is an anamorphic lens corresponding to each laser, the adjustment may be performed by displacing the position of the anamorphic lens. Further, focus adjustment may be performed in the entire system of the optical scanning device that has passed through the imaging optical system SA.

  As described above, in this embodiment, as described above, optical adjustment is performed in a light emission mode in which there is no influence of mode hopping due to self-heating such as a light emission duty of 20% or less, and the difference between the wavelength at the time of optical adjustment and the target wavelength λ3 is calculated. Minute, the optical adjustment value is shifted. Thus, in this embodiment, stable optical adjustment can be performed without taking a longer time than in the past.

  In the present embodiment, as described above, the target wavelength is set and adjusted on the shorter wavelength side than the intermediate wavelength between the wavelength λ2 in the actual use state of the optical scanning device and the wavelength λ1 immediately after lighting. This stabilizes the optical performance in a state where the image forming apparatus main body is frequently used, and prevents image quality deterioration such as the density of the halftone area of the image forming apparatus.

  FIG. 9 is a sectional view (sub-scanning sectional view) of the main part in the sub-scanning direction according to the second embodiment of the present invention. This figure shows a method for adjusting the conjugate relationship between the deflection surface and the surface to be scanned. In the figure, the same elements as those shown in FIG.

  The present embodiment is different from the first embodiment in that the second optical system SA includes the diffractive optical element 7E. Other configurations and optical functions are the same as those in the first embodiment, and the same effects are obtained.

  That is, in the figure, SA is an imaging optical system as a second optical system, and has an imaging lens 6E, a diffractive optical element (imaging lens) 7E, and three reflecting mirrors M5, M6, and M7. ing.

  In this embodiment, the light beam deflected and reflected by the optical deflector (polygon mirror) which is a deflecting means passes through the imaging lens 6E, and the optical path thereof is bent by the two reflecting mirrors M5 and M6 to reach the diffractive optical element 7E. In the diffractive optical element 7E, a light incident surface 701E is a refractive optical surface, and an output surface 702E is a diffractive optical surface.

  The light beam that has passed through the diffractive optical element 7E is further folded by the reflecting mirror M7 and guided to the surface to be scanned T1.

  As described above, each surface of the polygon mirror is tilted by a small angle in the sub-scanning direction, which causes so-called pitch unevenness in which the imaging position on the surface to be scanned rises and falls. In order to reduce pitch unevenness, it is necessary to make the vicinity of the deflection point (deflection surface) C0 of the polygon mirror and the surface to be scanned T1 optically conjugate in the sub-scan section.

  In this embodiment, by using an optical element (diffractive optical element) 7E in which a diffraction grating is formed on the surface of a plastic lens existing in the imaging optical system SA, the deflection surface C0 and the surface to be scanned T1 in the sub-scan section. Compensation temperature compensation is performed.

  Regarding the adjustment of the conjugate relationship, it is necessary to perform an optical adjustment in consideration of both the wavelength variation due to the manufacturing error of the semiconductor laser and the wavelength change due to the mode hop.

  It is conceivable to adjust the conjugate relationship by changing the optical path length. For example, it can be adjusted by displacing the position of the reflecting mirror (optical element) M7 optically closest to the surface to be scanned in the direction of arrow D shown in FIG.

  In the present embodiment, in order to perform optical adjustment with high accuracy, a polygon mirror 5 ′ that intentionally has a large surface tilt amount is used instead of the polygon mirror that is put into the product. The detection system uses a C-shaped slit 56 and a photosensor 55. At the time of detection, the height of the scanning line is detected from the time required to pass through the slits 1 and 2 constituting the C-shaped slit 56 (see FIG. 10).

  FIG. 10 shows the trajectory of the scanning line of the light beam deflected and reflected by the deflection surfaces 5a and 5b among the plurality of deflection surfaces (5a to 5d) of the polygon mirror 5 ′ shown in FIG.

  The state in which there is no time difference in the scanning time for the five scanning beams from the plurality of deflection surfaces 5a to 5e is the deflection point (deflection surface) C0 of the polygon mirror 5 'and the slit position T1 (that is, the photosensitive drum surface position that is the surface to be scanned). ) Is a conjugate relationship.

  Further, as a method for measuring the conjugate relationship without rotating the polygon mirror, a configuration using a jig mirror 57 for an adjustment tool as shown in FIG. 13 is also conceivable. The jig mirror 57 is divided into two regions of the right half 57R and the left half 57L of the incident light beam 58, and the angles of the reflecting surface in the main scanning direction and the sub scanning direction are slightly different in each region. The incident light beam reflected by the jig mirror 57 is reflected in the two directions of the light beam 58R and the light beam 58L, and two spot images are observed with a two-dimensional CCD or the like.

  When the conjugate relationship between the deflection surface and the surface to be scanned is deviated, the spot 59 on the surface to be scanned is broken into two states as shown in FIG. 14A, and the conjugate relationship is established. In this state, the spots 59 are aligned in the sub-scanning direction as shown in FIG. By determining the barycentric positions of the two spots 59, it can be determined whether or not they are in a conjugate relationship.

For example, two spot images are integrated in the sub-scanning direction. Then, as one LSF (line spread function), it is determined that the peak light amount value of the LSF is maximized or the state where the 1 / e ² slice diameter of the peak light amount value is minimized is in a conjugate relationship. It is also possible.

  Also in the present embodiment, it is necessary to perform the optical adjustment in the most frequently used state in the actual use state of the optical scanning device as in the first embodiment.

  Therefore, it is conceivable that the reflection mirror M7 is displaced by Δλ after adjusting the conjugate relation with respect to the wavelength λ1 immediately after the semiconductor laser is turned on by the adjustment method as described above. That is, the optical adjustment is performed again so that the optical adjustment value is shifted by an amount corresponding to the wavelength difference Δλ that satisfies the conditional expression (2).

  As another adjustment method, the position of the photosensor 55 may be offset in advance in a direction away from the optical scanning device by Δλ with respect to the scanned surface T1 in advance.

  Further, as shown in FIG. 9, the conjugate relationship can be adjusted by displacing the positions of at least some of the optical elements of the second optical system SA mounted on the optical scanning device. Furthermore, as shown in FIG. 15, the mounting position of the optical scanning device 11 itself can be adjusted by shifting (displacement) in the direction of arrow F in the figure relative to the image forming apparatus main body.

  In order to change the attachment position of the optical scanning device 11 to the image forming apparatus, it is possible to adjust the position by using, for example, a screw 60 shown in FIG.

  In FIG. 15, reference numeral 10 denotes a housing (optical box), which is attached to the mounting substrate 13 of the image forming apparatus main body by screws 60. Reference numeral 11 denotes an optical scanning device.

  FIG. 16 is a flowchart of optical adjustment of the optical scanning device in this embodiment.

  In this embodiment, first, an imaging lens, a diffractive optical element, a reflecting mirror, a polygon mirror, and an incident optical system (laser unit, focus adjusting cylinder lens, etc.) are attached to an optical box (housing) 10 (step 1). ).

  As described above, the adjustment of the conjugate relationship changes the optical path length, so that the focus position is shifted. Therefore, the fine adjustment of the focus is performed after adjusting the conjugate relationship. However, even if the conjugate relationship is adjusted in a state where there is no focus at all, the adjustment accuracy is lowered, so that rough adjustment may be required (step 2).

  The coarse focus adjustment is performed by shifting optical members such as a main scanning cylinder lens (not shown) and a sub-scanning cylinder lens (not shown) existing in the incident optical system and light source means such as a semiconductor laser in the optical axis direction. be able to.

  Next, the adjustment of the conjugate relationship is performed. As described above, the conjugate relationship adjustment may be performed by using a conjugate relationship adjustment jig polygon mirror having a large tilt amount of the surface in the sub-scanning direction (step 3). The jig reflection mirror 57 shown may be used. The semiconductor laser is turned on in the light emission mode 1 in which the wavelength is stable as in the first embodiment (step 4).

  The conjugate relationship is adjusted by, for example, moving the reflecting mirror M7 in the direction of arrow D shown in FIG. 9 using the light beam that is lit at the wavelength λ1 immediately after the semiconductor laser is lit (step 5). In this state, the conjugate relationship is adjusted to be the best at the wavelength λ1. Therefore, the reflection mirror M7 is offset in the direction of the arrow D by an amount corresponding to Δλ so that the conjugate relationship becomes the best at the target wavelength (wavelength satisfying the conditional expression (1)) λ3 (step 6).

  Next, the reflection mirror M7 is rotated in the direction of arrow E shown in FIG. 12 to adjust the height (irradiation position) of the scanning line on the surface to be scanned (step 7). Here, the reflecting mirror M7 is fixed (step 8), and the adjustment of the conjugate relationship and the irradiation position is completed.

  Next, the process moves to a focus position adjustment step. The jig polygon mirror used for adjusting the conjugate relation is replaced with the product polygon mirror (step 9), and the semiconductor laser is turned on again in the light emission mode 1 (step 10). For fine adjustment of the focus position, the same optical member as that used in step 2 may be used, or another optical member having low adjustment sensitivity may be used (step 11). In this state, the focus is adjusted to be the best at the wavelength λ1. Therefore, the adjustment value corresponding to Δλ is offset so that the best focus is obtained at the target wavelength (wavelength satisfying conditional expression (1)) λ3 (step 12). As a result, the optical adjustment is actually performed with the light beam having the target wavelength λ3. In this state, the optical member used for the focus adjustment is bonded and fixed to the optical box (step 13).

  As described above, in this embodiment, as described above, optical adjustment is performed in a light emission mode in which there is no influence of mode hopping due to self-heating such as a light emission duty of 20% or less, and the difference between the wavelength at the time of optical adjustment and the target wavelength is determined. The optical adjustment value is shifted. Thus, in this embodiment, stable optical adjustment can be performed without taking a longer time than in the past.

  In the present embodiment, as described above, the target wavelength is set and adjusted on the shorter wavelength side than the intermediate wavelength between the wavelength λ2 in the actual use state of the optical scanning device and the wavelength λ1 immediately after lighting. This stabilizes the optical performance in a state where the image forming apparatus main body is frequently used, and prevents image quality deterioration such as the density of the halftone area of the image forming apparatus.

[Color image forming apparatus]
FIG. 17 is a cross-sectional view of the main part in the sub-scanning direction showing the embodiment of the color image forming apparatus of the present invention. In the figure, reference numeral 100 denotes a color image forming apparatus. The color image forming apparatus 100 receives code data (R, G, B color signals) Dc from an external device 102 such as a personal computer. The code data Dc is converted into image data of different colors Yi (yellow), Mi (magenta), Ci (cyan), and Bki (black) by the printer controller 101 in the apparatus. The light is input to the optical scanning device 11 having the configuration shown. The light scanning device 11 emits a light beam modulated according to the image data Yi, Mi, Ci, Bki, and the light beams scan the photosensitive surfaces of the photosensitive drums 21 to 24 in the main scanning direction. The

  The photosensitive drums 21 to 24 serving as electrostatic latent image carriers (photoconductors) are rotated clockwise (R direction) by a motor (not shown). With this rotation, the photosensitive surfaces of the photosensitive drums 21 to 24 move in the sub-scanning direction orthogonal to the main scanning direction with respect to the light beam. Above the photosensitive drums 21 to 24, a charging roller (not shown) for uniformly charging the surface of the photosensitive drums 21 to 24 is provided so as to contact the surface. The surface of the photosensitive drums 21 to 24 charged by the charging roller is irradiated with a light beam scanned by the optical scanning device 11.

  As described above, the light beam is modulated based on the image data Yi, Mi, Ci, and Bki, and an electrostatic latent image is formed on the surface of the photosensitive drums 21 to 24 by irradiation with the light beam. Let me. This electrostatic latent image is developed into a toner image by developing units 31 to 34 disposed so as to contact the photosensitive drums 21 to 24 further downstream in the rotation direction of the photosensitive drums 21 to 24 than the irradiation position of the light beam. As developed.

  The toner images developed by the developing units 31 to 34 are temporarily formed on the intermediate transfer belt 103 disposed so as to be opposed to the photosensitive drums 21 to 24 above the photosensitive drums 21 to 24. Transferred to form a color image. The color toner image formed on the intermediate transfer belt 103 is transferred onto a sheet 108 as a transfer material by a transfer roller (transfer device) 104. The paper 108 is stored in a paper cassette 107.

  The sheet 108 to which the unfixed toner image is transferred is further conveyed to a fixing device. The fixing device includes a fixing roller 105 having a fixing heater (not shown) therein and a pressure roller 106 disposed so as to be in pressure contact with the fixing roller 105. As a result, the sheet 108 conveyed from the transfer unit is heated while being pressed at the pressure contact portion between the fixing roller 105 and the pressure roller 106 to fix the unfixed toner image on the sheet 108. Then, the fixed sheet 108 is discharged out of the image forming apparatus.

  A registration sensor 109 reads the Y, M, C, and Bk registration marks formed on the intermediate transfer belt 103 to detect the color misregistration amount of each color. By feeding back the detection result to the optical scanning device 11, it is possible to form a high-quality color image without color misregistration.

  Although not shown in FIG. 17, the print controller 101 performs not only the data conversion described above but also controls each unit in the image forming apparatus, a polygon motor in the optical scanning apparatus, and the like.

FIG. 3 is a main scanning sectional view of the optical scanning device according to the first embodiment of the present invention. FIG. 3 is a sub-scan sectional view of the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 3 is a sub-scan sectional view of the incident optical system of the optical scanning device according to the first embodiment of the present invention. Graph showing the wavelength change of the laser emitted by the adjustment tool Graph showing the change in wavelength of the laser emitted in the emission mode when using the product The figure explaining the relation between the depth center position and the surface to be scanned at each wavelength Sectional drawing of the principal part of the optical adjustment apparatus of Example 1 of this invention Flowchart of optical adjustment according to the first embodiment of the present invention The figure explaining the optical adjustment of Example 2 of this invention Diagram of a C-shaped slit used for optical adjustment of Example 2 of the present invention Cross section of the main part of the 5-sided polygon mirror The figure explaining the optical adjustment of Example 2 of this invention The figure explaining the optical adjustment of Example 2 of this invention The figure explaining the optical adjustment of Example 2 of this invention The figure explaining another method of the optical adjustment of Example 2 of this invention Flow chart of optical adjustment according to the second embodiment of the present invention 1 is a schematic view of a main part of a color image forming apparatus according to an embodiment of the present invention. Main part perspective view of a conventional optical scanning device Sectional view of the main part of a conventional optical scanning device The figure when the figure of an optical scanning device is written together with the laser emission sequence of Example 1 of this invention A graph depicting the relationship between the spot diameter and the position in the optical axis direction

Explanation of symbols

1A, 1B Light source means (semiconductor laser)
2A, 2B First optical system (anamorphic lens)
20 Binocular anamorphic lens 3A, 3B Aperture stop 5 Optical deflector 5 'Adjusting polygon mirror 5a-5d Deflection surface 6A, 6'A, 7A, 7B, 7'A, 7'B, 6E Imaging lens 7E Diffraction optics Element M1 to M6 Mirror 8A to 8D Scanned surface (photosensitive drum)
LA incident optical system SA second optical system (imaging optical system)
SR, SL Scan unit 9 Motor 10 Case (Optical box)
DESCRIPTION OF SYMBOLS 11 Optical scanning device 12 Laser unit 50 Adjustment tool 51 Jig cylinder lens 52 Jig spherical lens 53 Objective lens 54 Adjustment laser light emission circuit 55 Photo sensor 56 C-shaped slit 57 Jig mirror 58 Light flux 59 Spot 60 Adjustment screw 100 Color image formation Device 101 Printer controller 102 External device (personal computer)
103 Intermediate transfer belt 104 Transfer roller 105 Fixing roller 106 Pressure roller 107 Paper cassette
108 Transfer material (paper)
109 Registration Sensor

Claims (11)

A semiconductor laser, a first optical system for condensing a light beam emitted from the semiconductor laser, an optical deflector for deflecting and scanning the light beam from the first optical system, and deflected and scanned by the optical deflector In an adjustment method of an optical scanning device for adjusting each member constituting an optical scanning device having a second optical system that forms an image of a light beam on a surface to be scanned,
At least one of the first optical system and the second optical system has a diffractive optical element,
The oscillation wavelength immediately after turning on the semiconductor laser is λ1,
When the semiconductor laser is caused to emit light in the entire image region in the actual use state of the optical scanning device, and the wavelength after the oscillation wavelength of the light beam emitted from the semiconductor laser is stabilized is λ2,
(5λ1 + λ2) / 6 <λ3 <(λ1 + λ2) / 2
An optical scanning device adjustment method, wherein each member constituting the optical scanning device is optically adjusted at a wavelength of λ3 that satisfies the following conditions. At the time of the optical adjustment, a laser beam having an oscillation wavelength λ1 oscillated by the semiconductor laser is performed, and then an optical adjustment value adjusted by a light beam having a wavelength λ1 is used.
(Λ2-λ1) / 6 <Δλ <(λ2-λ1) / 2
2. The method of adjusting an optical scanning device according to claim 1, wherein the optical adjustment is performed again so as to shift the optical adjustment value by an amount corresponding to the wavelength difference Δλ that satisfies the following condition.   The first optical system includes a diffractive optical element, and in the optical adjustment, focus adjustment is performed by displacing a position of the optical element included in the first optical system or a position of the semiconductor laser. The method of adjusting an optical scanning device according to claim 1 or 2.   The second optical system includes a diffractive optical element, and in the optical adjustment, the optical deflector is displaced by displacing a position of an optical element included in the second optical system or a mounting position of the optical scanning device. 4. The method of adjusting an optical scanning device according to claim 1, wherein a conjugate relationship between the deflection surface of the optical scanning device and the surface to be scanned is adjusted. 5.   5. The method of adjusting an optical scanning device according to claim 1, wherein the emission duty of the semiconductor laser is set to 20% or less during the optical adjustment. A light beam oscillated from a semiconductor laser is condensed by a first optical system, the condensed light beam is deflected and scanned by an optical deflector, and the deflected and scanned light beam is scanned via a second optical system. In the adjustment method of the optical scanning device for adjusting each member constituting the optical scanning device that forms an image on the surface,
An adjustment method of an optical scanning device, wherein the emission duty of the semiconductor laser is set to 20% or less during optical adjustment.   7. The method of adjusting an optical scanning device according to claim 1, wherein the semiconductor laser is fixed to a holder made of resin. A semiconductor laser, a first optical system for condensing a light beam oscillated from the semiconductor laser, an optical deflector for deflecting and scanning the light beam from the first optical system, and a light beam deflected and scanned by the optical deflector And a second optical system that forms an image on the surface to be scanned,
At least one of the first optical system and the second optical system has a diffractive optical element,
The depth center position in the main scanning direction at the center of the image immediately after the semiconductor laser is turned on is Xm1, and the depth center position in the sub-scanning direction is Xs1,
In the actual use state of the optical scanning device, the semiconductor laser is oscillated all over the image area, and the depth center position in the main scanning direction at the image center after the oscillation wavelength is stabilized is Xm2, and the depth center position in the sub-scanning direction Is Xs2 and the scanned surface position is Xt.
(Xm1 + Xm2) / 2 <Xt <(5Xm1 + Xm2) / 6
Or
(Xs1 + Xs2) / 2 <Xt <(5Xs1 + Xs2) / 6
An optical scanning device satisfying at least one of the following expressions.   9. The optical scanning device according to claim 8, wherein the semiconductor laser is fixed to a holder made of resin.   An optical scanning device adjusted by the optical scanning device adjustment method according to claim 1 or an optical scanning device according to claim 8 or 9, and a photoconductor disposed on the surface to be scanned. A developing unit that develops an electrostatic latent image formed on the photosensitive member by a light beam scanned by the optical scanning device as a toner image, and a transfer unit that transfers the developed toner image to a transfer material. And a fixing device for fixing the transferred toner image to the transfer material.   The image forming apparatus according to claim 10, further comprising a printer controller that converts a signal input from an external device into image data.