JP2000111820A - Multibeam scanner, multibeam scanning method and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the magnification error of a scanning image-forming lens and to effectively reduce the fluctuation of a vertical line in a multibeam scan ner. SOLUTION: In this multibeam scanner, plural beams from plural light sources 11 and 12 which can be independently driven and modulated in accordance with an image signal are deflected at constant angular velocity by a deflector 16 common to the beams, and the deflected beams are condensed as light spots separated from each other in a subscanning direction on a surface to be scanned 18 by the common scanning image-forming lens 17, then plural lines on the surface to be scanned are simultaneously scanned nearly at constant velocity. In the device, plural light sources are selected so that ΔK and Δλ satisfy a condition: Δλ/[25.4×2/ δ×ΔK×θ}]<=1. Provided that ΔK and Δλ are the quantities defined by ΔK=(1/θ)(dL/dλ) when it is assumed that the angle of view equivalent to writing width is θ (rad), writing density is δ (dpi), the maximum wavelength difference between plural light sources is Δλ and the writing width corresponding to the angle of view: θ with the beam of use reference wavelength: λ is L (λ).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multi-beam scanning device, a multi-beam scanning method, a method of manufacturing a multi-beam scanning device, and an image forming apparatus.

[0002]

2. Description of the Related Art A plurality of beams (in this specification, "light beams") from a plurality of light sources which can be modulated and driven independently in accordance with image signals are respectively equalized by a deflector common to these beams. Deflected angularly, each deflected beam,
A multi-beam scanning device that uses a common scanning imaging lens to converge on the surface to be scanned as "light spots separated from each other in the sub-scanning direction" and simultaneously scan a plurality of lines on the surface to be scanned at substantially the same speed. Is being put to practical use. In an optical scanning device, the wavelength of a beam emitted from a semiconductor laser or an LED used as a light source (emission wavelength of a light source) varies among individual light sources due to manufacturing tolerances. Therefore, when a plurality of such light sources are used in a multi-beam scanning device, the emission wavelengths of the respective light sources are generally not exactly the same. If the light emission wavelength differs for each light source,
The chromatic aberration of magnification in the scanning imaging lens becomes a problem.

[0003] This problem will be specifically described with reference to FIG. In FIG. 1, reference numerals 11 and 12 indicate semiconductor lasers as light sources. These semiconductor lasers 11 and 12 are:
Modulation driving is performed independently in accordance with image signals. Each beam emitted from the semiconductor lasers 11 and 12 is converted into a “beam form suitable for the subsequent optical system” by the coupling lenses 13 and 14, respectively. Coupling lens 1
Each beam transmitted through 3 and 14 is converged in the sub-scanning direction by the cylinder lens 15, and each beam is formed as a long line image in the main scanning direction. The deflector 16 is a rotating polygon mirror in this example, has a deflecting / reflecting surface in the vicinity of the image forming position of each line image, and reflects each beam. Each of the reflected beams is deflected at a constant angular velocity with the constant speed rotation of the deflector 16, passes through the scanning imaging lens 17, and
The light condenses as light spots separated from each other in the sub-scanning direction on the surface to be scanned 18 (substantially, a photosensitive surface of a photoconductive photoconductor). The two beams deflected at a constant angular velocity by the deflector 16 are focused on the optical sensor 20 by the lens 19 and detected on the way to the writing area. The two beams to be deflected are also separated from each other in the main scanning direction, and are separately detected by “synchronous light detecting means” constituted by the lens 19 and the optical sensor 20.
Then, the start of writing is synchronized for each beam based on the detection result of the synchronous light detecting means.

The light scanning by each light spot is performed on the surface to be scanned 1.
8 at the write start position BG on “8”
The information for the line is written in a predetermined time. " As described above, the length written with the information for one line is called "write width". The writing width is originally determined as a design value of the device. At that time, the emission wavelength of the light source is determined by the standard of the semiconductor laser or the like used as the light source. The standard value of the emission wavelength assumed in the design is called "used reference wavelength" and is represented by "λ". As an example of the reference wavelength for use: λ, an emission wavelength of a semiconductor laser: 780 nm can be mentioned. The reference wavelength used is also a "standard value in light source manufacturing". Since the lens action of the scanning imaging lens 17 depends on the wavelength of light, the writing width depends on the emission wavelength of the light source, and the writing width determined as a design value is determined by the reference wavelength used: λ. This write width is represented as “reference write width: L (λ)”. In actuality, the emission wavelength of the light source varies from light source to light source as described above. If the emission wavelength of the light source deviates from the used reference wavelength: λ to λ ± Δλ (Δλ is a minute wavelength change), the actual writing width is set to L (λ
± Δλ), as shown in FIG. 1, it is different from the design reference write width: L (λ). As described above, each beam is detected on the way to the writing area, and the start of writing is synchronized. At this time, since the beam detection position by the synchronous light detecting means and the writing start position BG are relatively close to each other, the writing start position BG is substantially the same for each beam, and no deviation occurs. But,
On the write end side, a non-negligible “deviation” appears at the write end position FN due to a magnification error due to chromatic aberration.

For example, in the "apparatus for scanning with two beams" in FIG. 1, if each light spot scans a line adjacent to each other, as shown in FIG. And the writing end position FN2 by the other light spot is alternately shifted, so that when a vertical line (a straight line in the sub-scanning direction) is written in this portion, "vertical line fluctuation" occurs in which the line that should be a straight line fluctuates. Will do. As an example, as a light source, "use reference wavelength:
Let us consider a case where two semiconductor lasers each having λ of 780 nm are used in the multi-beam scanning apparatus shown in FIG. Variation in oscillation wavelength of the semiconductor laser: Δλ is ± 20 nm. Therefore, one of the oscillation wavelengths of the two semiconductor lasers used as the light source in the same multi-beam scanning device is 80
0 nm and the other could be 760 nm. In such a case, the design reference writing width: L (780 n
Considering 216 mm as m), the writing width: L (8
00 nm) and L (760 nm) have a difference of about 70 μm. The size of one dot which is “one unit of writing” by optical scanning is 63.5 at a writing density of 400 dpi.
In this case, 70 μm, which is the “shift” of the writing end position, is about the same as the size of one dot. In such a case, the “vertical line fluctuation” is hardly noticeable.
In recent years, there has been a demand for a higher writing density, and a writing density of 600 dpi (600 dots per inch) or more has been realized, and an extremely high writing density of 1200 dpi has been realized. 2400dp
Realization of writing densities of i and higher is also contemplated. For example, when a vertical line is written at 600 dpi, the size of one dot is 40 μm, and the 70 μm, which is the “maximum amplitude of fluctuation” of vertical line fluctuation, is 2 μm of the size of one dot.
It is less than twice, and the fluctuation of the vertical line is "to barely be recognized visually". According to the research conducted by the inventors, it has been found that the vertical line fluctuation becomes conspicuous when the maximum amplitude of the fluctuation is larger than twice the size of one dot.

As described above, the chromatic aberration has been described as the "magnification error of the scanning imaging lens" which causes vertical line fluctuation. However, the cause of the magni? Cation error is other than chromatic aberration. In a multi-beam scanning device, a plurality of beams are condensed as light spots on a surface to be scanned by a common scanning image forming lens. However, since a plurality of deflected beams are separated from each other in the sub-scanning direction, scanning is performed. The position at which the light passes through the image lens differs for each deflection beam, and this also causes a magnification error. Hereinafter, the magnification error in this case will be referred to as “magnification error due to the difference in the passing position”. As a measure for correcting the magnification error due to the chromatic aberration, it is conceivable to use an achromatic lens for the scanning imaging lens, but the cost of the scanning imaging lens increases. Further, when the scanning image forming lens includes a plastic lens, chromatic aberration correction is not always easy because there are few types of optical plastic materials.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce a magnification error due to the chromatic aberration and effectively reduce vertical line fluctuation in a multi-beam scanning apparatus.
Another object of the present invention is to reduce a vertical line fluctuation by reducing the magnification error due to the chromatic aberration and the magnification error due to the passing position difference in the multi-beam scanning apparatus.

[0008]

A multi-beam scanning apparatus is used to "deflect a plurality of beams from a plurality of light sources which can be independently modulated and driven in accordance with an image signal at a uniform angular velocity by a deflector common to these beams. Each of the deflected beams is condensed on the surface to be scanned by a common scanning image forming lens as light spots separated from each other in the sub-scanning direction, and a plurality of lines on the surface to be scanned are simultaneously scanned at substantially constant speed. Multi-beam scanning device ". The light source is a semiconductor laser or LED
It is of course possible to use a semiconductor laser as the light source (claim 9). As a deflector common to a plurality of beams, a rotating polygon mirror, a rotating dihedral mirror, or a rotating single mirror can be used. The multi-beam scanning device according to the first aspect has the following features.

That is, the angle of view corresponding to the writing width is θ (ra
d), the writing density is δ (dpi), the maximum wavelength difference between the plurality of light sources is Δλ, and the reference writing width corresponding to the above-mentioned angle of view: θ is L (λ) with a beam having the used reference wavelength: λ. Then δ
≧ 600 dpi. Further, the quantity defined by ΔK = (1 / θ) (dL / dλ): ΔK and the maximum wavelength difference: Δλ satisfy the following conditions: (1) 0 <Δλ / [25.4 × 2 / ｛δ × ΔK ×
The plurality of light sources are selected so as to satisfy θ｝ ≦ 1. As the “dL / dλ” in the definition of ΔK, in practice, a change in the writing width: L when the wavelength is shifted by 1 nm from the reference wavelength to be used: λ may be used.

The condition (1) is a condition that the difference in the writing width due to the beams from the two light sources having the maximum wavelength difference: Δλ is “less than twice the size of one dot” due to a magnification error due to chromatic aberration. That is, this is a condition in which the vertical line fluctuation is not conspicuous. That is, when (1 / θ) (dL / dλ) is substituted for ΔK, the expression (1) is as follows: 0 <Δλ · (dL / dλ) · δ / (25.4) ≦ 2, but Δλ · ( dL / dλ) is the above maximum wavelength difference:
Write width corresponding to Δλ: difference of L: ΔL (see FIG. 2)
It is. Therefore, Δλ · (dL / dλ) · δ / (25.
If 4) is rewritten as ΔL · δ / (25.4), this indicates how many times the above-mentioned ΔL corresponds to one dot at the writing density: δ. Therefore, the above condition (1) is a condition in which ΔL is equal to or less than twice the size of one dot. Since Δλ is the “maximum wavelength difference between a plurality of light sources”, even when there are three or more light sources, the wavelength difference between the light sources does not become larger than Δλ. Therefore, even when three or more lines are simultaneously written by three or more light sources, the above ΔL does not exceed twice as large as one dot. In order to satisfy the above condition (1),
Normally, it is necessary to measure the emission wavelength of each light source and select and combine the light sources that satisfy the condition (1). However, if a group of light sources having a small “wavelength variation” in process capability is used, wavelength measurement can be omitted. "Semiconductor laser fabricated from the same wafer" as multiple light sources
Is used (claim 2), since these have small variations in wavelength, there is no need to select by wavelength measurement.

According to a third aspect of the present invention, there is provided a multi-beam scanning apparatus.
It has the following features. That is, the modulation frequencies of the at least two light sources are made different from each other such that "the writing widths by the beams from these light sources become substantially equal" for at least two of the plurality of light sources. In writing by a light spot, assuming that the time for writing one dot is “T”, the modulation frequency of the light source for the light spot is defined as “1 / T”. Assuming that the length of one line written by writing in the light spot, that is, the above-described reference writing width: L is the length of N dots, the time required to write the effective writing width: L is “N
* T ". In writing using beams from the above two light sources (the light sources 1 and 2 are assumed to have the same modulation frequency), the actual writing width written by each beam is different from the magnification error (chromatic aberration and / or passing position difference). L (light source 1) ≠
Suppose L (light source 2). At this time, L (light source 2) / L
If (light source 1) = s, the time for writing one dot by the beam from light source 1 is T (light source 1), and the time when the beam from light source 2 is 1
Dot writing time: Assuming that s times T (light source 2), one dot written by the beam from light source 1 has a dot diameter in the main scanning direction s times larger than one dot written by the beam from light source 2. Therefore, regardless of the existence of the magnification error, the writing width of the beam from the two light sources can be the same. That is, the modulation frequency of the light source 2 is 1 / T
(Light source 2), the modulation frequency of the light source 1 may be 1 / {s · T (light source 2)}. The modulation frequency of the light source 1 cannot always be set exactly to 1 / {s · T (light source 2)}, but by satisfying a relationship approximating such a relationship with necessary accuracy, the light source 1 , 2 can be made substantially equal. As described above, in the multi-beam scanning device according to the third aspect, correction of a magnification error is caused by a chromatic aberration, a passing position difference, or a combination thereof. Is possible.

Such "correction of the magnification error by adjusting the modulation frequency" can be shared with the first or second aspect of the present invention. That is, in the multi-beam scanning apparatus according to claim 1 or 2, the at least two light sources of at least two of the plurality of light sources are so arranged that writing widths by beams from these light sources are substantially equal. The modulation frequencies can be different from each other (claim 4). Further, in the actual multi-beam scanning device, if the main cause of the magnification error is chromatic aberration, ΔL is known in advance according to the emission wavelength of the light source. In such a case, at least two of the plurality of light sources are used. For light sources, at least two light sources are used depending on the wavelength of each beam from these light sources.
The modulation frequencies of the two light sources are different from each other.
Thus, a magnification error with respect to the beams from these two light sources can be substantially eliminated. The multi-beam scanning device according to the sixth aspect is the third, fourth, or fifth aspect.
In the multi-beam scanning device according to the description, “a pair of optical sensors disposed on a writing start side and a writing end side by a deflected beam is provided. And means for determining the modulation frequency of the beam at the light source. " In the multi-beam scanning device according to any one of the first to sixth aspects, the scanning image forming lens can include "one or more plastic lenses" (claim 7).

Since the plastic lens is inexpensive, it can be manufactured at low cost, and a special lens surface shape such as an aspherical surface can be easily formed. Therefore, the plastic lens is suitable as a lens for a scanning imaging lens. However, since there are few types of optical plastic materials, it is difficult to correct “magnification error due to chromatic aberration” by achromatism. Therefore, the significance of applying the present invention to a multi-beam scanning device using a plastic lens in the scanning imaging lens is significant. The number of the plurality of light sources may be two (claim 8). Of course, the number of light sources may be three or more. In the inventions according to claims 3 to 5, the "two light sources" in the "at least two light sources" means that when the number of light sources is three or more, the two light sources in which a difference in writing width due to a magnification error appears most remarkably. It is. A multi-beam scanning device according to a tenth aspect has a plurality of light sources, a deflector, and a scanning imaging lens. The plurality of light sources can be modulated and driven independently according to the image signal.
The deflector reflects a plurality of beams from the plurality of light sources on a deflecting / reflecting surface, and deflects each beam at a constant angular velocity by rotating the deflecting / reflecting surface. This deflector is common to a plurality of beams. The scanning imaging lens converges the plurality of beams deflected by the deflector on the surface to be scanned as light spots separated from each other in the sub-scanning direction, and simultaneously makes the plurality of lines on the surface to be scanned substantially uniform in speed. Scan. The angle of view corresponding to the writing width is θ (rad), the writing density is δ (dpi), the maximum wavelength difference between a plurality of light sources is Δλ, and a beam having a used reference wavelength: λ corresponds to the angle of view: θ. Assuming that the writing width is L (λ), the plurality of light sources have an amount defined by ΔK = (1 / θ) (dL / dλ): ΔK and Δλ satisfy the following conditions: (1) 0 <Δλ /[25.4×2/｛δ×ΔK×
θ｝] ≦ 1.

In the multi-beam scanning device according to the tenth aspect, the writing density δ can be δ ≧ 600 dpi (claim 11) or δ ≧ 1200 dpi (claim 12), Furthermore, δ ≧ 2400d
pi (claim 13). The plurality of light sources may include a semiconductor laser.
4) An LED (light emitting diode) may be included (claim 15). The deflector can be a rotating polygon mirror (Claim 16), a "rotating single mirror" having one reflecting surface on one rotating flat mirror, or a "rotating two mirror having both reflecting surfaces." It can also be a "mirror" (claim 17). The rotating single-sided mirror and the rotating two-sided mirror have an advantage that a so-called sag can be substantially prevented since the spatial displacement between the deflecting reflection surface and the rotation axis is small. In the multi-beam scanning device according to the tenth aspect, at least one of the plurality of light sources may have a reference wavelength of 780 nm (claim 18), and furthermore, each of the plurality of light sources may be used. The reference wavelength may be 780 nm (claim 19).

According to a twentieth aspect of the present invention, in the multi-beam scanning apparatus according to the tenth aspect,
In writing at a writing density of δ of 600 dpi or more, “a plurality of light sources are prepared so as to remove vertical line fluctuation”. In the multi-beam scanning device according to the tenth aspect, the scanning imaging lens may have the following configuration. That is, the scanning imaging lens can have at least two lenses made of a plastic material having an “Abbe number of 40 or more and 80 or less” (claim 21). Further, the scanning imaging lens has at least two lenses, and for each of these lenses, the thickness at the center: t1 and the thickness at the periphery in the main scanning direction:
t2 may satisfy the following condition: (2) 0.3 ≦ t2 / t1 ≦ 1.7 (claim 22). FIG. 5 exemplifies a case where the scanning imaging lens is constituted by two lenses. The lens 17A has a center thickness: d ₁ and a peripheral portion thickness: d ₂ , and the lens 17B has a center thickness: d _2.
d ₁ ′ and thickness in the main scanning direction peripheral portion: d ₂ ′. In this case, “0.3 ≦ d ₂ / d ₁ ≦ 1.7” and “0.
3 ≦ d ₂ ′ / d ₁ ′ ≦ 1.7 ”.

Alternatively, the scanning image forming lens may be constituted by at least two lenses, and one of the two lenses may have a positive power and the other may have a negative power. (Claim 23). Furthermore, FIG.
As shown in (1), the scanning image forming lens 17 is composed of at least two lenses 17A and 17B, and the scanning image forming lens 17 is most deviated from the starting point of deflection of the deflector 16 (the intersection between the optical axis of the scanning image forming lens and the deflecting reflection surface). the distance to the exit surface of the lens 17A closest to the deflector 16: and l _1, the surface to be scanned 18 from the starting point of the deflection
Leading to the distance: l ₂ and is, conditions: can (3) so as to satisfy l ₁ / l ₂ ≧ 0.25 (claim 24). As shown in FIG. 7, the scanning image forming lens 17 is composed of at least two lenses 17A and 17B,
Principal ray of the deflected beam toward the write start position BG on the 8, corners measure the deflection angle when incident on the incident side of the closest lens 17A to the deflector 16 from the optical axis: the theta _1, the principal ray When the angle of incidence on the surface 18 to be scanned is measured from the optical axis to be an angle θ ₂ , these can satisfy the condition: (4) θ ₂ / θ ₁ ≧ 0.4. (Claim 25).

As described above, the condition that vertical line fluctuation caused by chromatic aberration of magnification is not conspicuous is as follows: 0 <Δλ · (dL / dλ) · δ / (25.4) ≦ 2 Difference: The tolerance for Δλ increases as “dL / dλ” decreases. Claim 2
1, the scanning imaging lens is "40 or more and 80
Having at least two lenses made of a plastic material having the following Abbe number, or satisfying the condition (2) as in claim 22;
The condition (3) should be satisfied as in claim 23, the lens having positive and negative power should be included in the scanning imaging lens as in claim 24, and the condition (4) as in claim 25. In all cases, satisfying the condition (1) effectively reduces the chromatic aberration of magnification itself and reduces the dL / d
λ ”is reduced. Therefore, Claims 21 and 2
By configuring the scanning imaging lens as shown in FIG. 5 (these can be implemented alone or in combination), the “tolerance of the wavelength difference between a plurality of light sources combined with each other” can be effectively set. Can be bigger.

A multi-beam scanning device according to a twenty-sixth aspect has a plurality of light sources, a deflector, and a scanning imaging lens. These are the same as those in the multi-beam scanning device according to the tenth aspect. 27. The multi-beam scanning apparatus according to claim 26, wherein at least two of the plurality of light sources have modulation frequencies of the at least two light sources such that writing widths by beams from the light sources are substantially equal. It is characterized by being different.
In the multi-beam scanning device according to claim 26,
The modulation frequencies of the at least two light sources can be different from each other so as to eliminate a magnification error of a writing width due to a wavelength difference between the light sources (claim 27). In addition, a pair of optical sensors provided on the writing start side and the writing end side by the deflection beam are provided, and the time when the deflection beam passes between these optical sensors by deflection is measured, and according to the measured time, A modulation frequency of the at least two light sources can be determined (claim 28). 27. The multi-beam scanning device according to claim 26, wherein the writing density: δ is equal to δ.
≧ 600 dpi (claim 29), δ ≧ 12
00 dpi (claim 30).
≧ 2400 dpi (claim 31).

Further, the plurality of light sources may include a semiconductor laser (claim 32), may include an LED (claim 33), and a rotating polygon mirror may be used as the deflector. (Claim 34) It is also possible to use a rotating single-sided mirror or a rotating two-sided mirror (Claim 35). In addition, at least one of the plurality of light sources may have an operating reference wavelength of 780 nm.
6) Alternatively, each of the plurality of light sources is used as a reference wavelength:
It can be 780 nm (claim 37).
The multi-beam scanning device according to claim 26, further comprises:
A plurality of light sources can be prepared so as to remove vertical line fluctuation in writing at a writing density: δ of 00 dpi or more (claim 38).

According to the multi-beam scanning method of the present invention, "a plurality of beams from a plurality of light sources which can be modulated and driven independently according to image signals are deflected at a uniform angular velocity by a deflector common to these beams. Method of condensing the deflected beam on the surface to be scanned by a common scanning imaging lens as light spots separated from each other in the sub-scanning direction, and simultaneously scanning a plurality of lines on the surface to be scanned at substantially the same speed. " It is. Claim 39
The described multi-beam scanning method uses such a scanning method to perform multi-beam scanning with substantially equal writing widths by limiting the difference in emission wavelength of at least two of the plurality of light sources. Features.
41. The multi-beam scanning method according to claim 40, wherein at least two of the beams from the plurality of light sources have different modulation frequencies of the light sources that emit the two beams such that the writing widths thereof are substantially equal. And performing multi-beam scanning. According to the method of manufacturing a multi-beam scanning device of the present invention, a plurality of light sources capable of being independently modulated and driven in accordance with an image signal, and a plurality of beams from the plurality of light sources are commonly used to deflect each beam at an equal angular velocity. The deflector and the respective deflectors deflected by the deflector converge the respective deflected beams on the surface to be scanned as light spots separated from each other in the sub-scanning direction. A step of preparing a scanning imaging lens for simultaneously scanning at substantially constant speed, and the plurality of light sources, deflectors,
Assembling the scanning image forming lens into a predetermined optical arrangement, wherein as a plurality of light sources to be assembled, an angle of view corresponding to a writing width: θ (rad), a writing density: δ (dpi),
Defined as ΔK = (1 / θ) (dL / dλ) as a writing width: L (λ) corresponding to the angle of view: θ with a beam having a maximum wavelength difference between a plurality of light sources: Δλ and a reference wavelength to be used: λ. The amount to be performed: ΔK and the above-mentioned Δλ satisfy the following conditions: (1) 0 <Δλ / [25.4 × 2 / ｛δ × ΔK ×
θ｝] ≦ 1 is selected, the plurality of light sources are selected.

The image forming apparatus of the present invention is an "image forming apparatus for forming a desired latent image by optical scanning of a latent image carrier, and developing and visualizing the formed latent image". The multi-beam scanning device according to any one of claims 1 to 38 is used as an optical scanning device that optically scans (Claim 42). As the latent image carrier, a "silver salt photographic film" or a "photoconductive photoreceptor" can be used. When a silver halide photographic film is used as a latent image carrier, a desired image can be obtained by developing a latent image formed by optical scanning with a multi-beam scanning device by a normal silver halide photographic process. Such an image forming apparatus can be specifically implemented as an optical plate making machine. When a photoconductive photoconductor is used as the latent image carrier, the latent image carrier is uniformly charged, then an electrostatic latent image is formed by writing by optical scanning, and the formed electrostatic latent image is developed. To obtain a toner image (claim 43). The toner image is fixed on the recording medium. As the photoconductive photoconductor, a sheet-shaped one such as zinc oxide paper may be used. In this case, the toner image can be fixed using the latent image carrier itself as a recording medium. Further, a toner image obtained by developing the electrostatic latent image formed on the latent image carrier can be transferred and fixed to a sheet-like recording medium (such as a transfer sheet or a plastic sheet for an overhead projector). Transferring the electrostatic latent image to the sheet-shaped recording medium and then developing;
The obtained toner image may be fixed on a recording medium.

The transfer of the toner image to the “sheet-shaped recording medium” may be performed directly from the latent image carrier to the recording medium, or may be performed via an intermediate transfer medium such as an intermediate transfer belt. The image forming apparatus can be specifically implemented as a digital copying machine, a digital plate making machine, an optical printer, or an optical plotter.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the invention will be described.

The following embodiments relate to the optical arrangement shown in FIG. Coupling lens 13,
The light beam coupled by the light source 14 can be a parallel light beam or a light beam having weak focusing or weak divergence. In the embodiments described below, the action of the coupling lenses 13 and 14 is “collimation”. Action "
The light beams from the light sources 11 and 12 are converted into parallel light beams. The data on the scanning imaging lens is as follows. As shown in FIG. 1, the scanning imaging lens 17 is composed of two lenses. These two lenses are called “first lens” and “second lens” from the side of the deflector 4 toward the surface to be scanned. Both surfaces of the first lens are “coaxial aspherical surfaces”. Coaxial aspherical surface, the optical axis coordinates X, the direction perpendicular to the optical axis of the coordinate r, the paraxial curvature radius R, the conic constant K, the aspherical coefficients of higher order A _4, A _6, A ₈ , A ₁₀ ,. . X = r ² / [R + R√ {1- (1 + K) r ² / R ² }] + A ₄ · r ⁴ + A ₆ · r ⁶ + A ₈ · r ⁸ + A ₁₀・ r
¹⁰ + .. _{In, R, K, A 4,} A 6, A 8, A 10,. . Given.

Data of the first lens Refractive index of material (plastic material for optics): N = 1.5244
1 (Wavelength: 780 nm) surface interval on the optical axis: D = 22.0 mm first surface coaxial aspherical shape (deflector-side lens surface of) R = -179.1, K = -1.267 , A 4 = 1.702E- 7, A ₆ = -3.926E-1
2, A ₈ = -2.564E-13, A ₁₀ = 4.493E-17, A ₁₂ = 1.6923E-21 Coaxial aspherical shape of the second surface (lens surface on the scanned surface side) R = -62.7, K = -0.041, A ₄ = 5.540E-7, A ₆ = -4.239E-11,
A ₈ = 1.994E-14, A ₁₀ = -3.779E-17
.

The shape of the second lens on both surfaces in the main scanning section (virtual plane section including the optical axis and orthogonal to the sub-scanning direction) is a "non-arc shape". For the non-circular shape, the coordinate in the optical axis direction is X, the coordinate in the main scanning direction is Y, the paraxial radius of curvature in the main scanning section is Rm, the conic constant is Km, and the higher order aspherical coefficients are a ₄ and a _6. , A ₈ , a ₁₀ ,. . As a well-known formula: X = Y ² /
[Rm + Rm√ {1- (1 + Km) r 2 / Rm 2}] + a 4 · r 4 + a 6 · r 6 + a 8 · r
^{_{8 + a 10 · r 10 +}} . . _{In, Rm, Km, a 4,} a 6, a 8,
a ₁₀ ,. . Given. Also, the radius of curvature in the sub-scanning section (imaginary plane section orthogonal to the main scanning direction): rs
Is the coordinate of the sub-scan section, Y is the radius of curvature on the optical axis (Y = 0), and the coefficients are b ₂ , b ₄ , b ₆ , b ₈ , b ₁₀ ,
b ₁₂ ,. . . As a polynomial: rs = Rs + b ₂ · Y ² + b ₄ · Y ⁴ + b ₆ · Y ⁶ + b ₈ · Y ⁸ + b ₁₀ · Y ¹⁰ + b
₁₂・ Y ¹² +. . . , Rs and coefficients are b ₂ , b ₄ , b ₆ , b ₈ , b ₁₀ ,. . . Given.

Data of second lens Refractive index of material (plastic material for optical use): N = 1.5244
1 (wavelength: 780 nm) Surface spacing on the optical axis: D = 3.5 mm Non-arc shape of the third surface (lens surface on the deflector side) Rm = -340.0, Km = -85.0, a ₄ = -6.765E-8 , A ₆ = -7.694E-12,
a ₈ = -1.163E-15, a ₁₀ = 1.593E-19 Curvature radius in the sub-scanning section of the third surface Rs = -31.6, b ₂ = 1.506E-3, b ₄ = -5.750E-7, b ₆ = 5.131E-1
1, b ₈ = 1.043E-14, b ₁₀ = -6.061E-18, b ₁₂ = 6.959E-22 Non-circular shape of the fourth surface (lens surface on the side to be scanned) Rm = -680.0, Km = 4.805 , A ₄ = -1.633E-7, a ₆ = -7.019E-1
2, a ₈ = -2.358E-16, a ₁₀ = 1.879E-20 Radius of curvature Rs = -16.68, b ₂ = b ₄ = b ₆ = b ₈ = b ₁₀ = b in the sub-scanning section of the fourth surface ₁₂ = 0
.

When the principal ray of the deflected light beam from the light source 11 matches the optical axis of the scanning imaging lens 17 when viewed from the sub-scanning direction, the distance between the starting point of deflection by the deflector 16 and the first surface: 45.8, distance between the second and third surfaces on the optical axis: 5
2.1, the distance between the fourth surface and the surface to be scanned on the optical axis: 105.5. In the above data display, for example, "E-8"
Means "10-8", and this numerical value depends on the immediately preceding numerical value. In the above data, the unit having the dimension of length is “mm”.

[0029]

Embodiment 1 In the case where the scanning imaging lens 17 of FIG. 1 has the above data,
The refractive index of the scanning imaging lens made of an optical plastic material changes by 0.00002 when the wavelength deviates from the reference wavelength of use: 780 nm by 1 nm. Angle of view: θ = 1.285r
ad, design reference write width: L (λ = 780 nm) = 21
6 mm. At this time, (dL / dλ) = 0.003
At 3981, ΔK = 0.0026445. Assuming that the writing density is δ = 1200 dpi, the wavelength difference satisfying the condition (1) is Δλ ≦ 12.4 nm. Therefore, Δλ =
Assuming 10 nm, the left side of the expression (1) is 0.8, which is sufficient to satisfy the conditional expression (1). So, for example,
As the light sources 11 and 12, the reference wavelength used is 780 nm,
If the wavelength difference between the light emission wavelengths is at most 10 nm, the vertical line fluctuation can be made almost invisible regardless of the presence of a magnification error caused by chromatic aberration. Also,
Writing density: If δ = 600 dpi, light sources 11 and 12
Wavelength difference allowed between: Δλ ≦ 24.8 nm, δ
Even in the case of = 2400 dpi, the problem of the vertical line fluctuation caused by the chromatic aberration of magnification can be substantially solved by combining the light sources 11 and 12 having the wavelength difference: Δλ of 5 nm or less.

That is, in the first embodiment described above, a plurality of beams from a plurality of light sources 11 and 12 which can be modulated and driven independently in accordance with an image signal are converted into a deflector 16 common to these beams.
Are deflected at the same angular velocity, and the respective deflected beams are condensed on the surface to be scanned 18 by the scanning image forming lens 17 as light spots separated from each other in the sub-scanning direction. In a multi-beam scanning device that scans at substantially constant speed, the angle of view corresponding to the effective writing width is θ
(= 1.285 rad), and the writing density is δ (= 1,200 d).
pi), when the maximum wavelength difference between a plurality of light sources is Δλ = 10 nm, and the writing width corresponding to the above-mentioned angle of view: θ is L (λ) = 216 mm with a beam having a reference wavelength of use: λ = 780 nm, δ ≧ 600 dpi and ΔK = (1 / θ) (d
L / dλ): The plurality of light sources 11 and 12 are selected so that the amount ΔK and the above Δλ satisfy the condition (1) (claim 1). The scanning imaging lens 17 is composed of two plastic lenses (claim 7), the number of light sources is two (claim 8), and the light sources 11, 1
Reference numeral 2 denotes a semiconductor laser. Normally, the specification of the wavelength variation of a semiconductor laser having a reference wavelength of 780 nm is ± 20 nm, but the wavelength variation in a semiconductor laser group manufactured from the same wafer is ± 4σ (σ:
(Standard deviation) is ± 1.1 nm, and the wavelength difference is only 2.2 nm in the range of ± 4σ, which satisfies the condition (1) sufficiently in terms of process capability (claim 2).

The multi-beam scanning device according to the first embodiment also includes a plurality of light sources 11 and 12 that can be independently modulated and driven in accordance with an image signal, and reflects a plurality of beams from the plurality of light sources by a deflecting reflecting surface. A deflector 16 common to a plurality of beams for deflecting each beam at a uniform angular velocity by rotation of the deflecting reflection surface, and the plurality of beams deflected by the deflector are scanned as light spots separated from each other in the sub-scanning direction. A scanning imaging lens 17 for converging light on the surface and simultaneously scanning a plurality of lines on the surface to be scanned at substantially the same speed, wherein an angle of view corresponding to the writing width is θ (rad), the writing density is To δ (d
pi), when the maximum wavelength difference between a plurality of light sources is Δλ, and the writing width corresponding to the angle of view: θ is L (λ) with a beam having a reference wavelength of use: λ, ΔK = (1 / θ) ( dL / dλ): ΔK and Δλ satisfy the following conditions: (1) 0 <Δλ / [25.4 × 2 / ｛δ × ΔK ×
A plurality of light sources 11 and 12 are selected so as to satisfy θ｝] ≦ 1 (claim 10), and the writing density: δ is δ = 600.
Alternatively, δ = 1200 or 2400 dpi (claims 11 to 13), the plurality of light sources 11 and 12 are semiconductor lasers (claim 14), and the deflector 16 is a rotating polygon mirror (claim 16). Each of the plurality of light sources 11 and 12 has a reference wavelength of 780 nm.
9) In writing at a writing density: δ of 600 dpi or more, the vertical line fluctuation is adjusted (claim 20).

In the first and second lenses (both plastic lenses) constituting the scanning image forming lens 17,
The Abbe number of the first lens is 55.5, and the Abbe number of the second lens is 55.5, both of which fall within the range of 40 to 80 (Claim 21). t1 = 2
2.0 mm, thickness in the peripheral portion in the main scanning direction: t2 = 14 mm
Where t2 / t1 = 0.64 and the center thickness of the second lens: t
1 = 3.5 mm, thickness at the peripheral portion in the main scanning direction: t2 = 2.
At 8 mm, t2 / t1 = 0.8, and both satisfy the condition (2). One of the first and second lenses (first lens) has a positive power, and the other (second lens)
Lens) has a negative power (claim 23), and the deflector 1
Distance from the starting point of deflection 6 to the exit side of the lens (first lens) closest to the deflector: l ₁ = 67.8 mm
And the distance from the starting point of deflection to the surface to be scanned: l ₂ = 22
Since it is 8.9, these ratios: l ₁ / l ₂ = 0.30, which satisfies the condition (3) (claim) 24. Further, the angles: θ ₁ and θ ₂ described with reference to FIG.
θ ₁ = 36.8 degrees, θ ₂ = 21 degrees, and their ratios are:
θ ₂ / θ ₁ = 0.57, thereby satisfying the condition (4) (claim 25).

Second Embodiment In the first embodiment described above, when the writing density: δ ≧ 1200, the light sources 11 and 12 use the reference wavelengths of 780 nm, and the difference between the emission wavelengths is Δλ. "12.4
smaller than μm ”must be used. In the case of a semiconductor laser having a reference wavelength of 780 nm, the variation in wavelength is about ± 20 nm. Therefore, in order to carry out Example 1, the reference wavelength used is 780 nm, and the difference in emission wavelength: Δλ is 12. It is necessary to select and use those smaller than 4 μm. According to the third aspect of the present invention, such sorting of the semiconductor laser is unnecessary.

In the case of the scanning imaging lens described above, Δλ = 20 n with respect to the reference wavelength used: 780 nm.
m, and a semiconductor laser having an emission wavelength of 760 nm (light source 1
1) and a semiconductor laser having an emission wavelength of 800 nm (light source 1).
Consider the case where 2) is used as a light source. In the scanning imaging lens specified by the above data, the reference wavelength used is 780 n
The writing width designed to be 216 mm for m is 215.944 for a semiconductor laser having an emission wavelength of 760 nm.
mm, a magnification error of -0.026% occurs, and
21 for a semiconductor laser with an emission wavelength of 0 nm.
6.012 mm, giving a magnification error of 0.006%. In this case, the writing end positions of the respective light spots are “a deviation of 68 μm” from each other in the main scanning direction.
When the resolution is 1200 dpi (the size of one dot: 21.2 μm), the above-mentioned shift is two dots or more, and vertical line fluctuation becomes conspicuous. At this time, 216.012 / 215.94
4 = 1.00031, the light source 12 (emission wavelength:
If the modulation frequency for the light source 12 is set to 1.00031 times the modulation frequency for the light source 11, the light source 12
Is the writing width by the light source 11: 215.
It is the same as 944 mm. That is, the magnification error for each light spot becomes the same, and vertical line fluctuation can be effectively eliminated. In this case, the difference between the writing width: 215.944 mm and the designed value: 216 mm does not pose any problem in practical use.

That is, in the second embodiment described above, a plurality of beams from a plurality of light sources 11 and 12 which can be modulated and driven independently in accordance with an image signal are converted into a deflector 16 common to these beams.
, Each beam is deflected at a constant angular velocity, and each deflected beam is condensed on a surface to be scanned 18 by a common scanning and imaging lens 17 as light spots separated from each other in the sub-scanning direction. In a multi-beam scanning apparatus that scans light sources at substantially the same speed simultaneously, a plurality of light sources 11, 1
In No. 2, the modulation frequencies of the two light sources 11 and 12 are different from each other so that the writing widths by the beams from these light sources are substantially equal (claim 3).
In the case of the second embodiment, the main cause of the magnification error is based on chromatic aberration, and the semiconductor lasers 11 and 12 used as light sources are used.
If the emission frequency of the light source is known in advance, the magnification error based on the chromatic aberration can be calculated in advance. Therefore, by making the modulation frequencies different from each other according to the emission wavelengths of the light sources 11 and 12, the writing width by the beam from each light source can be substantially reduced. (Claim 5). In the case where the cause of the magnification error is not necessarily caused by chromatic aberration, as in the invention according to claim 6, between a pair of optical sensors provided on the writing start side and the writing end side by the deflection beam, The modulation frequency of each beam at the light source can be determined according to the “time that each beam passes by deflection”.

An embodiment of the present invention will be described with reference to FIG. As shown in FIG. 3A, a pair of optical sensors 25 and 26 are provided on a writing start side and a writing end side of a portion which is an extension of the surface to be scanned 18, and a deflected beam from each light source is provided. When detected by the optical sensors 25 and 26, the outputs of the optical sensors 25 and 26 are as shown in FIG. Time: t ₁ is the time when the beam from the light source 11 passes between the optical sensors 25 and 26, and time: t ₂ is the time
This is the time when the beam from 2 passes between the optical sensors 25 and 26. Therefore, the modulation frequency of the light source 12 is set to (t ₁ / t ₂ ) times the modulation frequency of the light source 11, or conversely, the light source 1
If the modulation frequency of 1 is set to (t ₂ / t ₁ ) times the modulation frequency of the light source 12, the writing width of each beam becomes equal to each other, and vertical line fluctuation is effectively prevented. In the embodiment shown in FIG. 3, the outputs of the optical sensors 25 and 26 are input to the counter 27, A / D converted, and the times: t ₁ and t ₂ are counted. This count result is input to the calculator 28. The calculator 28 calculates (t ₁ / t ₂ ), changes the clock frequency in the clock generator 29 based on the result, and changes the clock frequency for driving the light source 11 (clock generator 31).
And applied to the LD drive circuit 32) (t ₁ /
Set the clock frequency t ₂ ) times. When the LD driving circuit 30 of the light source 12 is driven by using the clock frequency from the clock generator 29 as a modulation frequency, the light sources 11 and 12 are modulated at a desired modulation frequency, and the writing width of each beam is made equal. can do.

The second embodiment described above also includes a plurality of light sources 11 and 12 that can be independently driven for modulation in accordance with an image signal.
A plurality of beams from the plurality of light sources are reflected by a deflecting reflection surface, and the rotation of the deflecting reflection surface deflects each beam at an equal angular velocity. A scanning imaging lens 17 for converging the plurality of beams on the surface 18 to be scanned as light spots separated from each other in the sub-scanning direction and simultaneously scanning a plurality of lines on the surface to be scanned at substantially the same speed; A multi-beam scanning apparatus in which the modulation frequencies of the at least two light sources 11 and 12 are different from each other so that at least two of the plurality of light sources have substantially the same writing width by the beams from these light sources. (Claim 26),
The modulation frequencies of the at least two light sources 11 and 12 are different from each other so as to eliminate a magnification error of a writing width due to a wavelength difference between the light sources (claim 27). 1 deployed to
It has a pair of optical sensors 25 and 26, and the modulation frequency of at least two light sources 11 and 12 is determined according to the times t ₁ and t ₂ at which the deflected beam passes between these optical sensors by deflection (claim). Item 28). And the writing density: δ is δ
= 1200 dpi (claim 30), and the plurality of light sources 1
Reference numerals 1 and 12 denote semiconductor lasers (claim 32), and the deflector 16 is a rotary polygon mirror (claim 34).
Each of 1 and 12 has a reference wavelength of 780 nm (claim 37). That is, in the multi-beam scanning apparatus according to the second embodiment, a plurality of light sources are prepared so as to remove vertical line fluctuation in writing at a writing density: δ of 600 dpi or more (claim 38).

In the first embodiment described above, a plurality of beams from a plurality of light sources 11 and 12 which can be modulated and driven independently in accordance with an image signal are respectively separated at a uniform angular velocity by a deflector 16 common to these beams. Each scanning beam is deflected and condensed by a common scanning imaging lens 17 onto a surface to be scanned 18 as light spots separated from each other in the sub-scanning direction. In the multi-beam scanning method of scanning at a high speed, at least two of the plurality of light sources 11 and 12 are limited in the difference in the emission wavelength to perform the multi-beam scanning with substantially the same writing width. The method is performed (claim 3
9). In the second embodiment described above, a plurality of beams from a plurality of light sources 11 and 12 which can be modulated and driven independently in accordance with an image signal are deflected at a uniform angular velocity by a deflector 16 common to these beams. Then, the respective deflected beams are condensed on the surface to be scanned 18 as light spots separated from each other in the sub-scanning direction by the common scanning and imaging lens 17, and a plurality of lines on the surface to be scanned are simultaneously scanned at substantially the same speed. In the multi-beam scanning method, at least two of the beams from the plurality of light sources are modulated so that the writing widths thereof are substantially equal. A multi-beam scanning method for performing multi-beam scanning with different frequencies is performed (claim 40).

The multi-beam scanning apparatus as shown in FIG. 1 has a plurality of light sources 11 and 12 which can be modulated and driven independently in accordance with an image signal, and a plurality of beams from the plurality of light sources. Deflector 16 for deflecting at uniform angular velocity
Each of the deflected beams is condensed on the surface to be scanned as light spots separated from each other in the sub-scanning direction. A plurality of light sources to be assembled, including a step of preparing a scanning imaging lens 17 for scanning at substantially constant speed and a step of assembling the plurality of light sources, the deflectors, and the scanning imaging lens in a predetermined optical arrangement. Angles of view corresponding to the writing width: θ (rad) and writing density: δ (d
pi), a writing width corresponding to the above-mentioned angle of view: θ with a beam having a maximum wavelength difference between a plurality of light sources: Δλ, and a reference wavelength used: λ
As (λ), the quantity defined by ΔK = (1 / θ) (dL / dλ): ΔK and the above Δλ satisfy the following conditions: (1) 0 <Δλ / [25.4 × 2 / ｛δ × ΔK ×
θ｝] ≦ 1 can be achieved by a manufacturing method of selecting a plurality of light sources.

FIG. 8 shows an embodiment of the image forming apparatus of the present invention. This image forming apparatus is a laser printer. The laser printer 100 has a “photoconductive photoconductor formed in a cylindrical shape” as the latent image carrier 111. Around the latent image carrier 111, a charging roller 112 as a charging unit, a developing device 113, a transfer roller 11
4. A cleaning device 115 is provided. "Corona charger" can be used as the charging means. Further, a two-beam multi-beam scanning device 117 using the laser beams LB1 and LB2 is provided, and “exposure by optical writing” is performed between the charging roller 112 and the developing device 113.
It is supposed to do. 8, reference numeral 116 denotes a fixing device, reference numeral 118 denotes a cassette, reference numeral 119 denotes a pair of registration rollers, reference numeral 120 denotes a paper feed roller, reference numeral 121 denotes a conveyance path, reference numeral 122 denotes a pair of paper discharge rollers, reference numeral 123 denotes a tray,
Reference symbol P indicates a transfer sheet as a recording medium. The multi-beam scanning device 117 has been described in the first embodiment or the second embodiment. When performing image formation,
The latent image carrier 111, which is a photoconductive photoreceptor, is rotated clockwise at a constant speed, the surface thereof is uniformly charged by the charging roller 112, and the laser beams LB1, L
An electrostatic latent image is formed upon exposure by optical writing by B2. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed. This electrostatic latent image is reversely developed by the developing device 113, and a toner image is formed on the latent image carrier 111. Cassette 1 containing transfer paper P
Numeral 18 is detachable from the main body of the image forming apparatus 100, and in a state where it is mounted as shown in FIG. The leading end of the paper P has a pair of registration rollers 119.
Can be bitten. The registration roller pair 119 sends the transfer paper P to the transfer section in synchronization with the timing at which the toner image on the latent image carrier 111 moves to the transfer position. The transferred transfer paper P is superimposed on the toner image at the transfer section, and the toner image is electrostatically transferred by the operation of the transfer roller 114. The transfer paper P on which the toner image has been transferred is sent to the fixing device 116, where the toner image is fixed by the fixing device 116, passes through the conveyance path 121, and passes through the discharge roller pair 1
The sheet 22 is discharged onto the tray 123. The surface of the latent image carrier 111 after the transfer of the toner image is cleaned by the cleaning device 115 to remove residual toner, paper dust, and the like.

That is, the image forming apparatus shown in FIG. 8 is an image forming apparatus that forms a desired latent image by optical scanning of the latent image carrier 111, develops the formed latent image, and visualizes the latent image. A multi-beam scanning device according to any one of claims 1 to 38 (claim 42), wherein the latent image carrier 111 is a "photoconductive photoconductor" and is formed by optical scanning. The electrostatic latent image is visualized as a toner image (claim 43). In the embodiment described above with reference to FIGS. 1 to 3, the light sources 11 and 12 are brought close to each other so that the beams from the respective light sources enter the deflector without combining the beams. The present invention can be applied to the case of performing synthesis. For example, as shown in FIG. 4, when beams from semiconductor lasers 11 and 12 as light sources are coupled by coupling lenses 13 and 14 and multi-beam scanning is performed by each beam synthesized by a beam synthesizing prism 50. Needless to say, the present invention can be applied. In FIG. 4, the beam combining prism 50 is positioned at a position where the beam from the coupling lens 14 is incident by １ ／.
It has a wavelength plate 51 and a polarization separation film 52 inside the prism. The beam from the semiconductor laser 11 is coupled by the coupling lens 13, enters the beam combining prism 50, passes through the polarization splitting film 52, and exits from the beam combining prism 50. After the beam from the semiconductor laser 12 is coupled by the coupling lens 14, the polarization plane is turned by 90 degrees by the half-wave plate, and when the beam enters the beam combining prism 50, it is totally reflected by the prism surface and the polarization reflection surface 52. Are combined with the beam from the semiconductor laser 11 and emitted from the beam combining prism 50. The present invention can be applied not only to the case where the scanning imaging lens is formed of a glass lens, but also to the case where the number of light sources is three or more.

[0042]

As described above, according to the present invention, a novel multi-beam scanning device can be realized.

In the multi-beam scanning device according to the first, second, tenth to twenty-fifth aspects, it is possible to effectively reduce the vertical line fluctuation by reducing the magnification error caused by the chromatic aberration of the scanning image forming lens. The multi-beam scanning device according to any one of claims 3 to 6 and 26 to 38 can effectively eliminate a magnification error in the scanning imaging lens and effectively prevent vertical line fluctuation. Further, the multi-beam scanning method of the present invention enables multi-beam scanning in which vertical line fluctuation is effectively reduced. The image forming apparatus of the present invention has no vertical line fluctuation by using the multi-beam scanning device. A good image can be formed.

[Brief description of the drawings]

FIG. 1 is a diagram for describing a problem to be solved by the present invention in relation to a multi-beam scanning device to which the present invention can be applied.

FIG. 2 is a diagram for explaining vertical line fluctuation which is a problem to be solved by the invention.

FIG. 3 is a diagram for explaining a characteristic portion of one embodiment of the invention described in claim 5;

FIG. 4 is a diagram showing beam synthesis in a multi-beam scanning device.
It is a figure for explaining an example.

FIG. 5 is a diagram for explaining the invention according to claim 22;

FIG. 6 is a diagram for explaining the invention described in claim 24;

FIG. 7 is a diagram for explaining the invention according to claim 25;

FIG. 8 is a diagram for explaining an embodiment of the image forming apparatus of the present invention.

[Explanation of symbols]

 11, 12 Semiconductor laser as light source 13, 14 Coupling lens 15 Cylinder lens 16 Rotating polygon mirror as deflector 17 Scanning imaging lens 18 Scanned surface

Claims (43)

[Claims] A plurality of beams from a plurality of light sources which can be modulated and driven independently according to image signals are respectively deflected at a uniform angular velocity by a deflector common to these beams, and each deflected beam is subjected to a common scanning connection. In a multi-beam scanning device that converges on the surface to be scanned as light spots separated from each other in the sub-scanning direction by an image lens and simultaneously scans a plurality of lines on the surface to be scanned at substantially the same speed, The corresponding angle of view is θ (rad) and the writing density is δ
(Dpi), when a maximum wavelength difference between a plurality of light sources is Δλ, and a writing width corresponding to the above-mentioned angle of view: θ is L (λ) with a beam having a used reference wavelength: λ, δ ≧ 600 dpi, ΔK = (1 / θ) (dL / dλ) The quantity: ΔK and the above Δλ satisfy the following conditions: (1) 0 <Δλ / [25.4 × 2 / ｛δ × ΔK ×
A plurality of light sources are selected so as to satisfy θ｝] ≦ 1. 2. The multi-beam scanning device according to claim 1, wherein the plurality of light sources are semiconductor lasers manufactured from the same wafer. 3. A plurality of beams from a plurality of light sources which can be modulated and driven independently in accordance with an image signal are respectively deflected at a uniform angular velocity by a deflector common to these beams, and each deflected beam is subjected to a common scanning connection. In a multi-beam scanning device that converges on a surface to be scanned as light spots separated from each other in a sub-scanning direction by an image lens and simultaneously scans a plurality of lines on the surface to be scanned at substantially the same speed, a plurality of light sources are provided. Wherein at least two of the light sources have modulation frequencies different from each other such that writing widths by beams from the light sources are substantially equal. 4. The multi-beam scanning device according to claim 1, wherein at least two of the plurality of light sources are arranged such that writing widths by beams from these light sources are substantially equal. A multi-beam scanning device, wherein the modulation frequencies of two light sources are different from each other. 5. The multi-beam scanning apparatus according to claim 3, wherein at least two of the plurality of light sources are modulated according to the wavelength of each beam from these light sources. A multi-beam scanning device having different frequencies. 6. The multi-beam scanning device according to claim 3, further comprising a pair of optical sensors provided on a writing start side and a writing end side by using a deflected beam. A multi-beam scanning apparatus, comprising: means for determining a modulation frequency of each beam in a light source according to a time required for a beam to pass by deflection. 7. The multi-beam scanning device according to claim 1, wherein the scanning imaging lens includes one or more plastic lenses. 8. The multi-beam scanning device according to claim 1, wherein the number of light sources is two. 9. The multi-beam scanning device according to claim 1, wherein the light source is a semiconductor laser. 10. A plurality of light sources which can be modulated and driven independently in accordance with an image signal, and a plurality of beams from the plurality of light sources are reflected by a deflecting / reflecting surface. A deflector common to the plurality of beams to be deflected, and the plurality of beams deflected by the deflector are condensed on the surface to be scanned as light spots separated from each other in the sub-scanning direction. A scanning imaging lens for simultaneously scanning a plurality of lines at a substantially constant speed, wherein an angle of view corresponding to a writing width is θ (rad), and a writing density is δ
(Dpi), when the maximum wavelength difference between a plurality of light sources is Δλ, and a writing width corresponding to the above-mentioned angle of view: θ is L (λ) with a beam having a used reference wavelength: λ, ΔK = (1 / θ) The quantity defined by (dL / dλ): ΔK and the above Δλ satisfy the following conditions: (1) 0 <Δλ / [25.4 × 2 / ｛δ × ΔK ×
A plurality of light sources are selected so as to satisfy θ｝] ≦ 1. 11. The multi-beam scanning device according to claim 10, wherein the writing density δ is δ ≧ 600 dpi. 12. The multi-beam scanning apparatus according to claim 10, wherein the writing density δ is δ ≧ 1200 dpi. 13. The multi-beam scanning device according to claim 10, wherein the writing density: δ satisfies δ ≧ 2400 dpi. 14. The multi-beam scanning device according to claim 10, wherein the plurality of light sources include a semiconductor laser. 15. The multi-beam scanning device according to claim 10, wherein the plurality of light sources include LEDs. 16. The multi-beam scanning device according to claim 10, wherein the deflector is a rotary polygon mirror. 17. The multi-beam scanning device according to claim 10, wherein the deflector is a rotating single-sided mirror or a rotating two-sided mirror. 18. The multi-beam scanning apparatus according to claim 10, wherein at least one of the plurality of light sources has a reference wavelength used:
A multi-beam scanning device having a wavelength of 780 nm. 19. The multi-beam scanning apparatus according to claim 10, wherein each of the plurality of light sources has a reference wavelength of 780 nm. 20. The multi-beam scanning device according to claim 10, wherein at a writing density: δ of 600 dpi or more,
A multi-beam scanning device, wherein a plurality of light sources are prepared so as to remove vertical line fluctuation. 21. The multi-beam scanning apparatus according to claim 10, wherein the scanning imaging lens has at least two lenses made of a plastic material having an Abbe number of 40 or more and 80 or less. apparatus. 22. The multi-beam scanning device according to claim 10, wherein the scanning imaging lens has at least two lenses, each of which has a thickness at a central portion: t1 and a peripheral portion in a main scanning direction. A multi-beam scanning apparatus, wherein the thickness of the portion: t2 satisfies the condition: (2) 0.3 ≦ t2 / t1 ≦ 1.7. 23. The multi-beam scanning device according to claim 10, wherein the scanning imaging lens has at least two lenses, one of which has a positive power and the other of which has a negative power. A multi-beam scanning device. 24. The multi-beam scanning apparatus according to claim 10, wherein the scanning imaging lens has at least two lenses, and extends from a starting point of deflection of the deflector to an exit side of the lens closest to the deflector. distance: between l _1, the distance reaches the surface to be scanned from a starting point of the deflection: l ₂ and is the condition: (3) multi-beam scanning apparatus characterized by satisfying l ₁ / l ₂ ≧ 0.25 . 25. The multi-beam scanning apparatus according to claim 10, wherein the scanning image forming lens has at least two lenses, and a principal ray of the deflected beam directed to the writing start position on the surface to be scanned is most deflected. The deflection angle when the light is incident on the incident side surface of the lens close to the device is defined as an angle θ ₁ measured from the optical axis, and the angle at which the principal ray is incident on the surface to be scanned is measured as the angle θ ₂ from the optical axis. Where: (4) a multi-beam scanning apparatus characterized by satisfying the following condition: (4) θ ₂ / θ ₁ ≧ 0.4. 26. A plurality of light sources which can be modulated and driven independently in accordance with an image signal, and a plurality of beams from the plurality of light sources are reflected by a deflecting / reflecting surface. A deflector common to the plurality of beams to be deflected, and the plurality of beams deflected by the deflector are condensed on the surface to be scanned as light spots separated from each other in the sub-scanning direction. A scanning imaging lens for simultaneously scanning a plurality of lines at a substantially constant speed, wherein at least two of the plurality of light sources have substantially equal writing widths by beams from these light sources, A multi-beam scanning device, wherein the modulation frequencies of the at least two light sources are different from each other. 27. The multi-beam scanning apparatus according to claim 26, wherein the modulation frequencies of at least two light sources are different from each other so as to eliminate a magnification error of a writing width due to a wavelength difference between these light sources. Multi-beam scanning device. 28. A multi-beam scanning apparatus according to claim 26, further comprising a pair of optical sensors provided on a writing start side and a writing end side by a deflection beam, wherein the deflection beam is deflected between these optical sensors. A multi-beam scanning device, wherein the modulation frequencies of at least two light sources are determined according to the passing time. 29. The multi-beam scanning device according to claim 26, wherein the writing density δ is δ ≧ 600 dpi. 30. The multi-beam scanning device according to claim 26, wherein the writing density δ is δ ≧ 1200 dpi. 31. The multi-beam scanning device according to claim 26, wherein the writing density δ is δ ≧ 2400 dpi. 32. The multi-beam scanning device according to claim 26, wherein the plurality of light sources include a semiconductor laser. 33. The multi-beam scanning device according to claim 26, wherein the plurality of light sources include LEDs. 34. The multi-beam scanning device according to claim 26, wherein the deflector is a rotary polygon mirror. 35. The multi-beam scanning device according to claim 26, wherein the deflector is a rotating single-sided mirror or a rotating two-sided mirror. 36. The multi-beam scanning apparatus according to claim 26, wherein at least one of the plurality of light sources has a reference wavelength used:
A multi-beam scanning device having a wavelength of 780 nm. 37. The multi-beam scanning apparatus according to claim 26, wherein each of the plurality of light sources has a reference wavelength of 780 nm. 38. The multi-beam scanning apparatus according to claim 26, wherein at a writing density: δ of 600 dpi or more,
A multi-beam scanning device, wherein a plurality of light sources are prepared so as to remove vertical line fluctuation. 39. A plurality of beams from a plurality of light sources which can be modulated and driven independently in accordance with an image signal are deflected at a uniform angular velocity by a deflector common to these beams, and each deflected beam is subjected to a common scanning connection. In a multi-beam scanning method in which an image lens converges on a surface to be scanned as light spots separated from each other in a sub-scanning direction and simultaneously scans a plurality of lines on the surface to be scanned at substantially the same speed, A multi-beam scanning method comprising: performing a multi-beam scan with substantially equal writing widths by limiting a difference between emission wavelengths of at least two of them. 40. A plurality of beams from a plurality of light sources which can be modulated and driven independently in accordance with image signals are respectively deflected at a uniform angular velocity by a deflector common to these beams, and each deflected beam is subjected to a common scanning connection. In a multi-beam scanning method in which an image lens converges on the surface to be scanned as light spots separated from each other in the sub-scanning direction and simultaneously scans a plurality of lines on the surface to be scanned at substantially the same speed, 2 such that at least two of the beams have substantially the same write width.
A multi-beam scanning method comprising performing multi-beam scanning by changing the modulation frequencies of light sources that emit two beams. 41. A method for manufacturing a multi-beam scanning apparatus, comprising: a plurality of light sources which can be modulated and driven independently in accordance with an image signal; and a plurality of beams from the plurality of light sources. A deflector that deflects at an angular velocity, common to the respective deflection beams deflected by the deflector, and converges the respective deflection beams on the surface to be scanned as light spots separated from each other in the sub-scanning direction; A step of preparing a scanning imaging lens for simultaneously scanning a plurality of lines on the surface at substantially constant speed, and a step of assembling the plurality of light sources, deflectors, and scanning imaging lens in a predetermined optical arrangement. As a plurality of light sources to be assembled, an angle of view corresponding to a writing width: θ (rad), a writing density: δ
(Dpi), the maximum wavelength difference between the plurality of light sources: Δλ, the writing width corresponding to the above-mentioned angle of view: θ with a beam of the reference wavelength: λ: L (λ), ΔK = (1 / θ) (dL / dλ) is defined by the following equation: ΔK and Δλ satisfy the following conditions: (1) 0 <Δλ / [25.4 × 2 / ｛δ × ΔK ×
θ｝] ≦ 1. A method of manufacturing a multi-beam scanning device, wherein the plurality of light sources are selected so as to satisfy the following condition. 42. An image forming apparatus for forming a desired latent image by optical scanning of a latent image carrier and developing and visualizing the formed latent image, wherein the optical scanning device is an optical scanning device. An image forming apparatus using the multi-beam scanning device according to any one of the preceding claims. 43. The image forming apparatus according to claim 42, wherein the latent image carrier is a photoconductive photoconductor, and an electrostatic latent image formed by optical scanning is visualized as a toner image. Characteristic image forming apparatus.