JP2002311358A - Optical scanning method and optical scanner and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate overlapping of scanning lines in optical scanning that multibeam system reciprocating scanning is performed. SOLUTION: By simultaneously and reciprocatively deflecting a plurality of beams by a deflection means 6, a surface to be scanned 9 is uniformly and reciprocatively scanned. When it is assumed that the number of beams is N, time required for the scanning of effective writing width is T, one cycle of the reciprocation of the deflected beam is 2T0, T/T0 is K, pixel density in a subscanning direction is Dp (dpi), and an interval between adjacent scanning lines almost simultaneously scanned with a plurality of light spots is Pi (mm), optical scanning is performed by setting N, Dp, K and Pi to satisfy a condition: (1) N.(25.4 mm/Dp).(1-K)>(N-1).Pi at the end of the effective writing width on the returning side of the reciprocative scanning.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning method, an optical scanning device for performing the method, and an image forming apparatus using the optical scanning device.

[0002]

2. Description of the Related Art A light beam emitted from a light source is deflected by a deflecting means, and the deflected light beam is guided on a surface to be scanned by a scanning optical element such as an fθ lens to form a light spot.
Optical scanning devices that perform optical scanning are widely known in relation to image forming apparatuses such as optical printers, digital copying machines, plain paper facsimile machines, optical plate making machines and optical drawing apparatuses.

As a deflecting means for deflecting a light beam from a light source, a rotary polygon mirror has conventionally been the mainstream, but since the apparatus is large-scale, banding due to vibration, temperature rise,
There are problems such as noise and power consumption.

As a deflection means, a galvanomirror has been known as a method of swinging a deflection reflection surface. Recently, a micromirror that uses a micromachine technology to perform sinusoidal vibration of a resonant structure has been proposed, and by using this, the optical scanning device can be downsized, banding due to vibration, temperature rise, noise, and power consumption can be significantly reduced. Expected.

When the light beam is deflected by swinging of the deflecting / reflecting surface, the light beam is deflected in a reciprocating motion, so that light scanning can be performed not only on the forward path but also on the return path of the deflected light beam. The use of a device that can swing at high speed can further speed up optical scanning.

However, such a reciprocating scan includes:
There are also the following problems. That is, in general, the photosensitive surface of the photosensitive medium, which is the actual surface to be scanned, is subjected to main scanning by optical scanning while being sent in the sub-scanning direction. Therefore, the scanning line scanned by the main scanning slightly tilts in the sub-scanning direction on the photosensitive surface.

Since the moving speed of the photosensitive surface in the sub-scanning direction is smaller than the speed of the main scanning, the inclination of the scanning line is very small. In optical scanning using a rotating polygon mirror, the direction of optical scanning by a light spot is fixed in one direction, and the inclination of scanning lines for each main scan is the same, and the scanning lines are parallel to each other. The slope of the line is practically irrelevant.

However, when the reciprocating scanning is performed, the inclination of the scanning line is reversed for each scanning, so that the scanning line draws a “zigzag line” on the photosensitive surface. In other words, the interval between the scanning lines written on the surface to be scanned causes a "difference between image heights of the scanning line intervals" which varies depending on the image height of the light spot, which causes density unevenness. In addition, in the case of multi-beam optical scanning, if scanning lines overlap with each other on the return side of reciprocating scanning, resolution may be reduced.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the overlap of scanning lines in optical scanning for performing reciprocal scanning in a multi-beam system. It is another object of the present invention to reduce a deviation between image heights of scanning line intervals on a surface to be scanned.

[0010]

According to a first aspect of the present invention, there is provided an optical scanning method comprising the steps of: "a plurality of light beams emitted from a plurality of light sources are deflected by a common deflecting means, and the plurality of deflected light beams are shared by a common scanning optical element. A plurality of light spots separated from each other in the sub-scanning direction on the surface to be scanned, and the plurality of light spots simultaneously scan a plurality of scanning lines on the surface to be scanned. Scanning method ", characterized by the following points. That is, the scanning surface is reciprocally scanned at a constant speed by simultaneously reciprocating a plurality of light beams by the deflecting means.

The number of light beams is N, the time required for scanning the effective writing width is T, and one reciprocating cycle of the deflected light beam is 2
T0 and T / T0 are K, and the pixel density in the sub-scanning direction is Dp (d
pi), when an interval between adjacent scanning lines scanned almost simultaneously by a plurality of light spots is Pi (mm), N, Dp,
When K and Pi are “the end of the effective writing width on the return side of the reciprocating scan”, the condition is as follows: N · (25.4 mm / Dp) · (1−K)> (N−1) · Pi (1) Are set such that the optical scanning condition is satisfied.

As described above, the optical scanning method according to the first aspect is a "multi-beam method" optical scanning method. The above parameter: K is the ratio of the time during which the light beam reciprocally deflected scans the effective writing width in the forward path or the return path. Condition (1) is a condition for preventing overlapping of the scanning lines.

According to a second aspect of the present invention, there is provided an optical scanning method comprising the steps of: "deflecting a light beam emitted from a single light source by a deflecting means, and guiding a plurality of deflected light beams onto a surface to be scanned by a scanning optical element; An optical scanning method for forming a light spot on a surface to be scanned and scanning the surface to be scanned "is characterized by the following points.

That is, the light beam is reciprocally deflected by the deflecting means, so that the surface to be scanned is reciprocally scanned at a constant speed. When the time required for scanning the effective writing width is T and one cycle of reciprocation of the deflected light beam is 2T0, these T and T0
Are set to satisfy the condition: T / T0 <0.7 (2).

The condition (2) means that the time for scanning the effective writing width in the forward or backward path of the light beam reciprocally deflected is 7 times the time for moving in the forward or backward path.
That is, the time is shorter than 0%.

In the optical scanning method according to the first or second aspect, when the deflection of the light beam by the deflecting means is performed in a sinusoidal manner, the light beam is deflected when passing substantially the center of the effective writing width. It is preferable that the absolute value of the angular velocity of the light beam is maximized (claim 3). With this configuration, the shift amount of the scanning line interval from the center of the effective writing width can be equally distributed to the left and right, so that a symmetric image can be formed, and density unevenness and resolution degradation are reduced. can do.

An optical scanning device according to a fourth aspect is an apparatus for implementing the optical scanning method according to the first aspect. That is, this optical scanning device `` deflects a plurality of light beams emitted from a plurality of light sources by a common deflecting means, and guides the deflected light beams to a surface to be scanned by a common scanning optical element. An optical scanning device that forms a plurality of light spots separated from each other in the sub-scanning direction on the surface to be scanned, and simultaneously scans a plurality of scanning lines on the surface to be scanned with the plurality of light spots,
It has a plurality of light sources, a deflection unit, and a scanning optical element.

The "plural light sources" emit a light beam for performing multi-beam scanning on the surface to be scanned. The plurality of light sources may be, for example, a plurality of independent semiconductor lasers, and each light beam emitted from these may be “beam-synthesized” and guided to the deflecting unit. A “semiconductor laser array” monolithically arranged may be used as a “plurality of light sources”.

The "deflecting means" deflects light beams emitted from a plurality of light sources back and forth. The “scanning optical element” guides a plurality of light beams deflected by the deflecting unit onto the surface to be scanned, and forms a plurality of light spots on the surface to be scanned. At this time, an optical system arranged on an optical path from the light source to the surface to be scanned is set so that a plurality of light spots formed on the surface to be scanned are separated from each other in the sub-scanning direction.

The scanning optical element also has a "function to make scanning by a light spot uniform". The number of light fluxes is N, the time required for scanning the effective writing width is T, and the round trip of the deflected light flux is 1
When the period is 2T0, T / T0 is K, the pixel density in the sub-scanning direction is Dp (dpi), and the interval between adjacent scanning lines scanned almost simultaneously by a plurality of light spots is Pi (mm),
N, Dp, K, and Pi are “the end of the effective writing width on the return side of the reciprocating scanning”, and the condition is: N · (25.4 mm / Dp) · (1-K)> (N−1) · Pi (1) is set.

In this case, among N, Dp, K and Pi,
N, Dp, and Pi are given as design conditions, and K can be set so as to satisfy the condition (1) (claim 5). Of these, N, Dp, K, and Pi can be set. ,
N, Dp, and K are given as design conditions.
Pi may be set so that the condition (1) is satisfied (claim 6).

An optical scanning device according to a seventh aspect is an apparatus for implementing the optical scanning method according to the second aspect. That is, this optical scanning device `` deflects a light beam emitted from a single light source by a deflecting means, guides a plurality of deflected light beams onto a surface to be scanned by a scanning optical element, and An optical scanning device that forms a light spot and scans a surface to be scanned, comprising a single light source, a deflecting unit, and a scanning optical element.

A "single light source" emits a light beam for optical scanning. As a single light source, a “semiconductor laser” is preferable. The “deflecting means” deflects the light beam emitted from the light source back and forth. The “scanning optical element” has a function of guiding the light beam deflected by the deflecting unit onto the surface to be scanned, forming a light spot on the surface to be scanned, and making scanning by the light spot uniform. Assuming that the time required for scanning the effective writing width is T and one cycle of reciprocation of the deflected light beam is 2T0, these T and T0 satisfy the condition: T / T0 <0.7 (2) Is set.

In the optical scanning device according to any one of claims 4 to 7, when the deflecting means is a device that deflects the light beam in a sinusoidal manner, the deflected light beam has substantially the effective writing width. It is preferable that the absolute value of the angular velocity of the deflected light beam is set to be maximum when passing through the center (claim 8).

In the optical scanning device according to the eighth aspect,
The deflecting means may be of a type that swings the deflecting reflection surface. Examples of the method of swinging the deflecting / reflecting surface include a galvanometer mirror and the above-mentioned “micro mirror that performs sinusoidal vibration of the resonance structure” (claim 9).

In the optical scanning device according to the ninth aspect,
The deflecting means (of the method of oscillating the deflecting reflection surface) includes a oscillating mirror for oscillating the deflecting reflection surface, and a fixed mirror disposed opposite to the oscillating mirror. (Multiple reflection of the deflected light beam between the surface and the fixed mirror) ".

In the case of the optical scanning device according to the tenth aspect,
One fixed mirror may be used, but two fixed mirrors are used.
The fixed mirrors of the surfaces are arranged in the sub-scanning direction, the `` tilt angle in the sub-scanning section '' of each fixed mirror is reversed, and the distance between the mirror surface of each fixed mirror and the deflecting reflection surface of the oscillating mirror is In the sub-scanning cross section, it is possible to set so as to increase toward the gap between the two, so that the deflected light beam is emitted from the gap.

The optical scanning device according to the ninth aspect has a "line image forming optical system for forming a light beam from the light source side near the position of the deflecting and reflecting surface of the deflecting means as a long line image in the main scanning direction". (Claim 12).

The "scanning optical element" can be composed of one or more lenses or one or more imaging mirrors. One or more lenses and one or more imaging mirrors can be used. It can also be configured with a mirror.

An image forming apparatus according to the present invention is an "image forming apparatus for forming an image by optically scanning a photosensitive medium", wherein the optical scanning according to any one of claims 4 to 12 is used for optically scanning a photosensitive medium. A scanning device is used (claim 13).

As the "photosensitive medium", various known ones can be used. For example, an image can be formed by using a chromogenic photographic paper, which develops color by heat, as a photosensitive medium, optically scanning the photographic paper, and developing a color using "heat energy" by a light spot.

Depending on the photosensitive medium, a latent image can be formed on the photosensitive medium by optical scanning, and the latent image can be visualized to form an image.
In this case, for example, a silver salt film can be used as the photosensitive medium. The latent image formed by optical scanning on the silver halide film is developed and processed according to the "normal silver halide photography process".
Fixing can be performed. Such an image forming apparatus includes:
It can be implemented as an optical plate making device or an optical drawing device.

A "photoconductive photoreceptor" can be used for the photosensitive medium. In this case, the latent image is formed as an electrostatic latent image, visualized as a toner image, and the toner image is "finally carried on a sheet-shaped recording medium".
5). If a known zinc oxide photosensitive paper is used as the photoconductive photoreceptor, the toner image formed on the zinc oxide photosensitive paper can be fixed as it is “using the zinc oxide photosensitive paper as a sheet-shaped recording medium”.

When a photoconductive photoreceptor that can be used repeatedly is used, the toner image formed on the photoreceptor is transferred to a sheet-like recording medium such as transfer paper or an OHP sheet (a plastic sheet for an overhead projector). Transfer directly or through an intermediate transfer medium such as an intermediate transfer belt,
By fixing, a desired image can be obtained.

These image forming apparatuses can be implemented as digital copiers, optical printers, optical plotters, facsimile machines and the like.

When the light beam is deflected by the swing of the deflecting / reflecting surface, the deflection light beam is "inclined with respect to a plane orthogonal to the oscillation axis of the deflecting / reflecting surface".
As a method of effectively reducing such scanning line bending, the scanning optical element may include one or more lenses in which a line connecting the sagittal vertices of the lens surface curves in the sub-scanning direction.

[0037]

FIG. 1 is a view for explaining an embodiment of an optical scanning device. FIG. 1A shows a state in which the optical arrangement of the optical scanning device is viewed from the sub-scanning direction, and FIG. 1B shows a state in which the optical arrangement is viewed from the main scanning direction.

The light beam radiated from the light source unit denoted by reference numeral 1 is converted into a parallel light beam by the collimating action of the coupling lens 2, and when passing through the aperture 3, the light beam peripheral portion is shielded and “beam-shaped”, and the light beam is cylindrically shaped. The light enters the lens 4.

The cylindrical lens 4 focuses the incident parallel light beam in the sub-scanning direction. The light beam transmitted through the cylindrical lens 4 is incident on the incident mirror 5 while being focused in the sub-scanning direction, is reflected, and is incident on the deflecting means 6.

The deflecting means 6 reflects the light beam incident from the incident mirror 5 and deflects the reflected light beam. The light beam deflected by the deflecting means 6 has its optical path direction corrected by the optical path direction correcting mirror 7 and passes through the lenses 8A and 8B. The lenses 8A and 8B constitute a "scanning optical element" and guide the deflected light beam to the surface 9 to be scanned (substantially, a photosensitive surface of a photosensitive medium) to form a light spot on the surface to be scanned. Form.

The deflecting means 6 deflects the reflected light beam in a reciprocating manner.
It reciprocates in the main scanning direction, and performs optical writing on the surface to be scanned on both the outward path and the return path.

The incident mirror 5 and / or the optical path direction correcting mirror 7 may be omitted depending on the layout of the optical system. Although the case where the function of the coupling lens 2 is a collimating function has been described, the form of the coupled light beam may be a “weak focused light beam” or a “weak divergent light beam”.

As the light source 1, a single semiconductor laser or a semiconductor laser array can be used. If a single semiconductor laser is used as the light source unit 1, optical scanning will be of a single beam type, and if a semiconductor laser array is used as the light source unit 1, optical scanning will be of a multi-beam type.

FIG. 1C is an explanatory diagram showing a main part of the deflecting means 6. A main part of the deflecting means 6 is a oscillating mirror 6A for oscillating the deflecting reflection surface around an "axis parallel to the sub-scanning direction", and two fixed mirrors arranged opposite to the oscillating mirror 6A. 6B and 6C, for multiple reflection of the deflecting light beam between the deflecting reflection surface of the oscillating mirror 6A and the fixed mirrors 6B and 6C.

As shown in FIG. 1D, two fixed mirrors 6 are provided.
B and 6C are arranged in the sub-scanning direction (z direction), and are in the sub-scanning section (a virtual plane section including the swing axis of the oscillating mirror 6A and orthogonal to the main scanning direction; xz shown in FIG. 1D). Angle of the fixed mirrors 6B and 6C (with respect to the sub-scanning direction) in the plane
θ _B and θ _C are opposite to each other, and the distance between the mirror surfaces of the fixed mirrors 6B and 6C and the deflecting reflection surface of the oscillating mirror 6A is set so as to increase toward the gap between them in the sub-scan section. And
The deflected light beam exits from the gap.

That is, as shown in FIG. 1D, the light beam reflected by the incident mirror 5 is directed to the deflecting / reflecting surface of the oscillating mirror 6A and to a plane orthogonal to the oscillating axis of the oscillating mirror 6A. After being incident obliquely and reflected by the deflecting reflecting surface, the fixed mirrors 6A, 6A
B and the deflecting and reflecting surface are repeatedly reflected and multiple-reflected, and the deflection angle is enlarged.
Inject from Note that the swing of the swing mirror 6A is simple and the swing angle changes in a sinusoidal manner.

By deflecting by the deflecting means such as the deflecting means 6, the direction of the deflected light beam can be separated from the direction of the incident light beam, and the skew (twist) of the deflected light beam can be effectively reduced. If skew occurs in the deflecting light beam, the wavefront aberration of the deflecting light beam deteriorates and the diameter of the light spot cannot be reduced. The diameter of the light spot can be reduced.

The "operation optical element" constituted by the lenses 8A and 8B makes the speed of the light spot formed by the "deflection light beam deviating sinusoidally" on the surface to be scanned uniform as described above. Are set with optical characteristics.

Hereinafter, according to a specific example, the conditions: (1),
(2) will be described. 1. Specific Example In the optical scanning device having the configuration shown in FIG. In the reciprocating scanning at substantially the same time, the pixel density in the sub-scanning direction: Dp = 1200 dpi, the interval between adjacent scanning lines scanned almost simultaneously by two light spots: Pi = 0.021.
2 mm, parameter: K (= T / T0) = 0.
It was set to 75.

In FIG. 2, arrow α indicates the direction of displacement of the photosensitive medium for sub-scanning. The lines indicated by reference signs A1 and B1 are
The two light spots are scanning lines to be written on the surface to be scanned in the “outgoing path” of the reciprocating deflection, and the lines indicated by reference numerals A2 and B2
The two light spots are scanning lines to be written on the surface to be scanned in the "return path" of the reciprocating deflection.

As shown in the figure, at the right end of the effective writing width (the end on the return side of the reciprocating scanning), the scanning lines B1 and A
2 overlaps. Such "overlapping scanning lines"
Causes image defects such as density unevenness and resolution degradation.

The above condition (1), ie, N · (25.4 mm / Dp) · (1-K)> (N−1) ·
When the left side and the right side of Pi are found, N = 2 and Dp = 1200 dp
i, Pi = 0.0212 mm, K (= T / T0) = 0.
75, the left side: 2 (25.4 mm / 1200) · (1-0.7
5) = 0.0106 mm Right side: (2-1) · 0.0212 mm = 0.0212 mm, and left side <right side. In FIG. 2, the distance: ξ represents the size of the “right side”, and the distance: η represents the size of the “left side”. That is, in the above specific example, the condition (1) is not satisfied.

[0053]

Embodiment 1 In view of the above results, in the above specific example, the parameter: K
Was changed to K = 0.42. At this time, condition (1)
Are the left side and the right side of the left side: 2 (25.4 mm / 1200) · (1-0.4
2) = 0.0246 mm Right side: (2-1) · 0.0212 mm = 0.0212 mm In this case, the state of the scanning lines formed on the surface to be scanned is shown in FIG. 3 according to FIG. The size of the above left side:
η, the size of the right side: ξ, the magnitude relationship is inverted from FIG.
The condition (1) is satisfied.

As shown in FIG. 3, in the first embodiment, the scanning lines do not overlap, and the effective writing width is set small (this is the result of setting the parameter: K small). ), The “deviation of the scanning line interval due to the image height” is reduced, and image defects such as density unevenness and resolution degradation can be reduced. Further, when the “deviation of the scanning line interval” falls within ± 70% or less, the image quality is further improved. From this viewpoint, the right side of the condition (1) is replaced by the following condition: 0 0.7N (25.4 mm / Dp) · (1-K)> (N−1) · Pi (3)

Embodiment 2 In the optical scanning device having the configuration shown in FIG. 1, a two-channel (number of light emitting sources: 2) semiconductor lasers (accordingly, the number of light beams: N = 2) is used as the light source unit 1, and the scanning surface 9 is used. In the case where the two scanning lines are reciprocally scanned substantially simultaneously, the pixel density in the sub-scanning direction: Dp = 1200 dpi, the interval between adjacent scanning lines scanned almost simultaneously by two light spots: Pi = 0.09
mm, parameter: K (= T / T0) = 0.7
Set to 5. FIG. 4 shows a state of a scanning line written on the surface to be scanned at this time, as shown in FIG.

When the left side and the right side of the condition (1) are obtained, the left side is 2 (25.4 mm / 1200) · (1−0.7
5) = 0.0106 mm Right side: (2-1) · 0.009 mm = 0.09 mm, and the left side> the right side, and the condition (1) is satisfied.
As can be seen from FIG. 4, no overlapping of the scanning lines occurs, so that image defects such as density unevenness and resolution degradation can be reduced.

In the second embodiment, the value of K (0.75) is the same as that in the above-described specific example (FIG. 2), but the interval between adjacent scanning lines scanned almost simultaneously by two light spots: Pi , The overlapping of the scanning lines is eliminated.
However, the “deviation of the scanning line interval” is larger than in the case of the first embodiment. Third Embodiment In the optical scanning device having the configuration shown in FIG. 1, a single semiconductor laser is used as the light source unit 1 and the surface 9 to be scanned is a single beam. This is a case in which reciprocating scanning is performed by the method.

When there is one light source, the scanning lines written on the surface to be scanned do not "overlap" each other, and there is no image deterioration due to the overlapping of the scanning lines described above. By controlling the deviation to ± 70% or less, image defects such as density unevenness and resolution degradation can be effectively reduced.

Since the deviation of the scanning line interval becomes ± 70% or less, the condition is (2).

FIG. 5 shows the state of the scanning line written by the reciprocating scanning of the single beam system according to the third embodiment. At this time, the value of K (= T / T0) is 0.67.

At this time, the deviation of the scanning line interval becomes ± 67% or less, and the density unevenness caused by the “scanning line interval deviation”
Image defects such as resolution degradation were effectively reduced.

In the specific examples described above and Examples 1 to 3,
The deflecting means is for "oscillating the oscillating mirror in a sine wave".
At this time, the vertical axis represents the deflection angle of the oscillating mirror: θ, and the time: T
Is plotted on the horizontal axis, the relationship between θ (degrees) and T is as shown in FIG.

In the portion indicated by reference numeral 7-1, the absolute value of the angular velocity of the oscillating mirror, which is the time derivative of the deflection angle: θ, becomes maximum,
Therefore, the absolute value of the angular velocity of the deflected light beam also becomes maximum.

In all of the first to third embodiments, the absolute value of the angular velocity of the deflected light beam is set to be maximum when the deflected light beam passes through substantially the center of the effective writing width. The amount of deviation of the scanning line interval from the center can be evenly distributed to the left and right, so that symmetric image formation can be achieved, and density unevenness and resolution degradation can be reduced.

When the position where the angular velocity of the deflected light beam becomes maximum deviates from the center of the effective writing width, for example, in a single beam optical scanning, the state of the scanning line written on the surface to be scanned is as follows. FIG. 6 shows a solid line. In this case, as apparent from FIG. 6, the "deviation of the scanning line interval" is asymmetric with respect to the center of the effective writing width.

That is, in FIG. 6, the value of the parameter: K is K = 0.67 as in the third embodiment, but “the position where the absolute value of the angular velocity of the deflected light beam is maximum is the effective writing width of the effective writing width. Because it is shifted from the center, the “shift amount of the scanning line interval” is different between the left and right with respect to the center of the effective writing width, resulting in an asymmetric image. In particular, since the area on the left side of FIG. 6 and the interval between the scanning lines change significantly alternately, the degradation of the resolution becomes extremely large.

FIG. 8 shows an embodiment of the image forming apparatus. This image forming apparatus is a “laser printer”.

The “laser printer” has a “photoconductive photosensitive member formed in a cylindrical shape” as the photosensitive medium 10. Around the photosensitive medium 10, a charging unit 11 (corona charger is illustrated, of course, a contact-type charging roller may be used), a developing device 13, and a transfer unit 14 (a type using corona discharge is used). Although shown, a contact-type transfer roller may be used), and a cleaning device 15 is provided.

The optical scanning device 1 using the laser beam LB
2 is provided to perform “exposure by optical writing” between the charging roller 11 and the developing device 13. In FIG. 8, reference numeral 16 denotes a fixing device, and reference numeral S denotes transfer paper as a “sheet-shaped recording medium”.

When an image is formed, the photosensitive medium 10, which is a photoconductive photosensitive member, is rotated clockwise at a constant speed, the surface thereof is uniformly charged by the charging means 11, and
Is exposed by the optical writing of the laser light beam LB, and an electrostatic latent image is formed. The formed electrostatic latent image is a so-called “negative latent image”
And the image area is exposed.

This electrostatic latent image is reversely developed by the developing device 13, and a toner image is formed on the photosensitive medium 10.
The transfer paper S is sent to the transfer unit at the same time as the toner image on the photosensitive medium 10 moves to the transfer position, and is superposed on the toner image at the transfer unit. Electrotransferred.

The transfer paper S to which the toner image has been transferred is sent to the fixing device 16, where the toner image is fixed in the fixing device 16 and discharged outside. The surface of the photosensitive medium 10 after the transfer of the toner image is cleaned by the cleaning device 15 to remove residual toner, paper dust, and the like.
The above-described OHP sheet can be used instead of the transfer paper, and the transfer of the toner image can be performed via an “intermediate transfer medium” such as an intermediate transfer belt.

By using the optical scanning devices of the first, second and third embodiments described above as the optical scanning device 12,
Good image formation can be performed.

Embodiments 1 and 2 described above use a “two-channel semiconductor laser array” as the light source unit 1 in the optical configuration shown in FIG. The plurality of light fluxes are deflected by the common deflecting means 6, and the deflected light fluxes are guided onto the surface 9 to be scanned by the common scanning optical elements 8A and 8B, so that the light beams are projected onto the surface 9 to be scanned in the sub-scanning direction. To form a plurality of light spots separated from each other, and the plurality of light spots
A plurality of light sources 1, a plurality of light sources 1, a deflecting unit 6 for reciprocatingly deflecting light beams emitted from the plurality of light sources, and a plurality of light beams deflected by the deflecting unit. Scanning optical elements 8A and 8B for guiding light on the surface 9 to be scanned, forming a plurality of light spots on the surface 9 to be scanned, and making scanning by the light spots uniform; (= 2), the time required to scan the effective writing width is T, and one cycle of reciprocation of the deflected light beam is 2T0, T
/ T0 is K, the pixel density in the sub-scanning direction is Dp (dpi),
When the interval between adjacent scanning lines scanned almost simultaneously by a plurality of light spots is Pi (mm), N, Dp, K, Pi
However, at the end of the effective writing width on the turnback side of the reciprocal scanning, the following condition is satisfied: N · (25.4 mm / Dp) · (1−K)> (N−1) · Pi (1) (Claim 4).

In the first embodiment, N, Dp, K, Pi
Among them, N, Dp, and Pi are given as design conditions, and K is set so as to satisfy the condition (1) (claim 5). In the second embodiment, N, Dp, K, P
Among i, N, Dp, and K are given as design conditions, and Pi is set so that the condition (1) is satisfied (claim 6).

Therefore, the optical scanning devices of the first and second embodiments deflect the plurality of light beams emitted from the plurality of light sources 1 by the common deflecting means 6, and deflect the plurality of deflected light beams to the common scanning optical element 8A. , 8B to form a plurality of light spots separated from each other in the sub-scanning direction on the surface 9 to be scanned, and a plurality of scanning lines on the surface 9 to be scanned by the plurality of light spots. In the optical scanning method of scanning simultaneously, the scanning target surface 9 is reciprocally scanned at a constant speed by simultaneously deflecting a plurality of light beams by the deflecting means 6 simultaneously.
The number of light beams is N, the time required for scanning the effective writing width is T, one cycle of reciprocation of the deflected light beam is 2T0, and T / T0 is K,
The pixel density in the sub-scanning direction is Dp (dpi), and the interval between adjacent scanning lines scanned almost simultaneously by a plurality of light spots is Pi.
(Mm), N, Dp, K, and Pi are set at the end of the effective writing width on the turnback side of the reciprocal scanning. Condition: N · (25.4 mm / Dp) · (1-K)> (N-1) · Pi (1) An optical scanning method (claim 1) is set and performed so as to satisfy (1).

Further, in the third embodiment, in the optical configuration shown in FIG.
The light beam emitted from the single light source 1 is deflected by the deflecting means 6, and the plurality of deflected light beams are guided onto the surface 9 to be scanned by the scanning optical elements 8A and 8B. An optical scanning device which forms a light spot on a surface to be scanned 9 and scans the surface to be scanned 9, comprising a single light source 1 and a deflecting means 6 for reciprocally deflecting a light beam emitted from the light source 1.
The scanning optical elements 8A and 8B guide the light beam deflected by the deflecting means 6 onto the surface 9 to be scanned, form a light spot on the surface 9 to be scanned, and equalize the speed of scanning by the light spot. When the time required for scanning the effective writing width is T and one cycle of reciprocation of the deflected light beam is 2T0, these T and T0 satisfy the condition: T / T0 <0.7 (2) The optical scanning device is set so as to satisfy the following.

Then, the light beam emitted from the single light source 1 is deflected by the deflector 6 by this optical scanning device.
In the optical scanning method of guiding a plurality of deflected light beams onto the surface to be scanned 9 by the scanning optical elements 8A and 8B to form a light spot on the surface to be scanned 9 and scanning the surface to be scanned 9, When the light beam is reciprocally deflected by the means 6, the surface 9 to be scanned is reciprocally scanned at a constant speed, and the time required for scanning the effective writing width is T, and one cycle of reciprocation of the deflected light beam is 2T0. An optical scanning method (claim 2) is performed in which T and T0 are set so as to satisfy the condition: T / T0 <0.7 (2).

In all of the first to third embodiments, the deflecting means 6
Is used to deflect the light beam in a sinusoidal oscillation manner, and is set so that the absolute value of the angular velocity of the light beam to be deflected becomes maximum when the deflected light beam passes through substantially the center of the effective writing width. Therefore, in the optical scanning devices of the first to third embodiments, the light beam is deflected by the deflecting means 6 in a sinusoidal oscillation manner, and the deflected light beam passes through substantially the center of the effective writing width. Sometimes, the absolute value of the angular velocity of the light beam to be deflected is maximized. "

In all of the optical scanning devices according to the first to third embodiments, the deflecting means 6 is of a type which oscillates the deflecting / reflecting surface (claim 9). A swing mirror 6A to be rotated, and a fixed mirror disposed opposite to the swing mirror 6A, and multiple-reflects the deflecting light beam between the deflection reflecting surface of the swing mirror 6A and the fixed mirror. (Claim 10) The fixed mirrors 6B and 6C are arranged in two planes in the sub-scanning direction, and the inclination angles θ _A and θ _{B of the} fixed mirrors in the sub-scanning section are opposite to each other, and the mirror surfaces of the fixed mirrors are opposite to each other. And the distance between the oscillating mirror and the deflection reflecting surface
In the sub-scan section, it is set so as to increase toward the gap between the two, and the deflected light beam is emitted from the gap.

In each of the optical scanning devices of the first to third embodiments, the light beam from the light source side is placed near the position of the deflecting reflection surface of the deflecting means 6.
There is a line image forming optical system 4 for forming a long line image in the main scanning direction.

The image forming apparatus according to the embodiment shown in FIG. 8 is an image forming apparatus for forming an image by optically scanning the photosensitive medium 10, and performs the optical scanning on the photosensitive medium 10 according to claims 4 to 1.
An optical scanning device according to any one of (2) to (13), wherein a latent image is formed on the photosensitive medium by optical scanning of the photosensitive medium, and the latent image is visualized (claim). 14), the photosensitive medium 10 is a photoconductive photoconductor, a latent image is formed as an electrostatic latent image, visualized as a toner image, and the toner image is finally carried on the sheet-shaped recording medium S (claim) Item 15).

To supplement the description a little, the optical scanning devices of the above-described embodiments are arranged side by side in the main scanning direction, and the effective writing width of each optical scanning device is connected to reduce the effective writing width. It may be increased.

In the first to third embodiments, the oscillating mirror of the deflecting means uses a sine-wave oscillating mirror. However, the oscillating mirror does not necessarily have to sine-wave oscillate. Further, in each of the embodiments, the light flux is reflected a plurality of times by the deflecting means to increase the effective writing width. However, it goes without saying that the configuration may be such that the deflecting means reflects only once. .

[0085]

As described above, according to the present invention, a novel optical scanning method and apparatus and an image forming apparatus can be realized. In the optical scanning method and apparatus according to the present invention, a deflecting means for performing reciprocal scanning is used, so that a small micromirror can be used. Can significantly reduce banding, temperature rise, noise, and power consumption.

[0086] Since the overlapping of the scanning lines on the surface to be scanned can be eliminated and the deviation between the scanning lines can be reduced, the density unevenness can be reduced and the resolution can be improved. Can be realized.

Therefore, the image forming apparatus of the present invention can form a good image by using the optical scanning device of the present invention.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of an optical configuration of an optical scanning device.

FIG. 2 is a diagram illustrating a state of a scanning line written on a surface to be scanned by a specific example optical scanning device that does not satisfy a condition (1).

FIG. 3 is a diagram illustrating a state of a scanning line written on a surface to be scanned by the optical scanning device according to the first embodiment.

FIG. 4 is a diagram illustrating a state of a scanning line written on a surface to be scanned by an optical scanning device according to a second embodiment.

FIG. 5 is a diagram illustrating a state of a scanning line written on a surface to be scanned by an optical scanning device according to a third embodiment.

FIG. 6 shows the position at which the angular velocity of the deflected light flux is maximum,
FIG. 8 is a diagram illustrating a state of a scanning line written on a surface to be scanned in optical scanning when the effective scanning width deviates from a central portion.

FIG. 7: Deflection angle: θ and time: T of an oscillating mirror that oscillates sinusoidally
FIG.

FIG. 8 is a diagram illustrating an embodiment of an image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source part 2 Coupling lens 3 Aperture 4 Cylindrical lens 6 Deflection means 8A, 8B Lens which comprises a scanning optical element 9 Surface to be scanned

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C362 AA07 AA10 BA17 BA56 BA71 BA82 2H045 AB24 AB62 BA02 BA22 BA23 BA33 CA62 5C051 AA02 CA07 DA02 DB02 DB22 DB24 DB30 DC04 DC07 DE09 DE26 FA01 5C072 AA03 BA17 HA02 HA06 HA09 HA05 H08 WA08 XA01 XA05

Claims (15)

[Claims] A plurality of light beams emitted from a plurality of light sources are deflected by a common deflecting means, and the plurality of deflected light beams are guided onto a surface to be scanned by a common scanning optical element. A plurality of light spots separated from each other in a sub-scanning direction are formed on a surface, and the plurality of light spots are used to simultaneously scan a plurality of scanning lines on the surface to be scanned. By reciprocating deflection, the surface to be scanned is reciprocally scanned at a constant speed, the number of light beams is N, the time required for scanning the effective writing width is T, and one cycle of reciprocation of the deflected light beam is 2T0, T / When T0 is K, the pixel density in the sub-scanning direction is Dp (dpi), and the interval between adjacent scanning lines scanned substantially simultaneously by a plurality of light spots is Pi (mm), the above N, Dp, K, and Pi are expressed as follows: Reciprocating scanning of the above effective writing width At the folded end, setting is performed so that the following condition is satisfied: N · (25.4 mm / Dp) · (1-K)> (N−1) · Pi (1) Light scanning method. 2. A light beam emitted from a single light source is deflected by a deflecting means, and a plurality of deflected light beams are guided onto a surface to be scanned by a scanning optical element to form a light spot on the surface to be scanned. In the optical scanning method for scanning the surface to be scanned, the light beam is reciprocally deflected by the deflecting means, so that the surface to be scanned is reciprocally scanned at a constant speed, and the time required for scanning the effective writing width is T. When one cycle of reciprocation of the deflected light beam is 2T0, T and T0 are set and performed so as to satisfy the condition: T / T0 <0.7 (2). Scan method. 3. The optical scanning method according to claim 1, wherein the light beam is deflected by the deflecting means in a sinusoidal manner, and is deflected when the deflected light beam passes substantially the center of the effective writing width. An absolute value of an angular velocity of a light beam to be maximized. 4. A light beam emitted from a plurality of light sources is deflected by a common deflecting means, and the deflected light beams are guided to a surface to be scanned by a common scanning optical element. An optical scanning device that forms a plurality of light spots separated from each other in a sub-scanning direction on a surface, and simultaneously scans a plurality of scanning lines on the surface to be scanned with the plurality of light spots. Deflecting means for reciprocally deflecting the light beams emitted from the plurality of light sources; and guiding the plurality of light beams deflected by the deflecting means onto the surface to be scanned to form a plurality of light spots on the surface to be scanned. A scanning optical element for making the scanning by the light spot at a constant speed, wherein the number of light beams is N, the time required for scanning the effective writing width is T, and one cycle of reciprocation of the deflected light beam is 2T0, T / T0 is K,
The pixel density in the sub-scanning direction is Dp (dpi), and the interval between adjacent scanning lines scanned almost simultaneously by a plurality of light spots is Pi.
(Mm), N, Dp, K, and Pi are the conditions at the end of the effective writing width on the turnback side of the reciprocating scan: N · (25.4 mm / Dp) · (1-K )> (N−1) · Pi (1) 5. The optical scanning device according to claim 4, wherein N, Dp, and Pi among N, Dp, K, and Pi are given as design conditions. An optical scanning device characterized by being set to be satisfied. 6. The optical scanning device according to claim 4, wherein N, Dp, and K among N, Dp, K, and Pi are given as design conditions. An optical scanning device characterized by being set to be satisfied. 7. A light beam emitted from a single light source is deflected by a deflecting means, and a plurality of deflected light beams are guided to a surface to be scanned by a scanning optical element to form a light spot on the surface to be scanned. An optical scanning device that scans the surface to be scanned, comprising: a single light source; deflecting means for reciprocatingly deflecting a light beam emitted from the light source; and a light beam deflected by the deflecting means. A scanning optical element that guides light on the scanning surface, forms a light spot on the surface to be scanned, and makes scanning by the light spot at a constant speed. Assuming that one cycle of the reciprocating light beam is 2T0, these T and T0 are:
Condition: An optical scanning device set to satisfy T / T0 <0.7 (2). 8. The optical scanning device according to claim 4, wherein the deflecting means deflects the light beam in a sinusoidal manner, and the deflected light beam is substantially at the center of the effective writing width. Wherein the absolute value of the angular velocity of the deflected light beam is set to be maximum when passing through the optical scanning device. 9. The optical scanning device according to claim 8, wherein the deflecting means is of a type that swings the deflecting reflection surface. 10. The optical scanning device according to claim 9, wherein the deflecting means has a oscillating mirror for oscillating the deflecting reflection surface, and a fixed mirror arranged opposite to the oscillating mirror. An optical scanning device, wherein a deflected light beam is reflected multiple times between a deflecting reflection surface of a moving mirror and a fixed mirror. 11. The optical scanning device according to claim 10, wherein the fixed mirrors are arranged in two planes in the sub-scanning direction, and the inclination angles of the fixed mirrors in the sub-scanning cross section are opposite to each other, and the mirror surfaces of the fixed mirrors are opposite. The distance between the mirror and the deflecting reflecting surface of the oscillating mirror is set so as to increase toward the gap between the two in the sub-scanning section, and the deflecting light beam is emitted from the gap. apparatus. 12. The optical scanning device according to claim 9, wherein the light beam from the light source is located near the position of the deflecting reflection surface of the deflecting means.
An optical scanning device comprising a line image forming optical system for forming a long line image in a main scanning direction. 13. An image forming apparatus for forming an image by optically scanning a photosensitive medium, wherein the optical scanning apparatus according to any one of claims 4 to 12 is used for optically scanning the photosensitive medium. Image forming device. 14. An image forming apparatus according to claim 13, wherein a latent image is formed on said photosensitive medium by optical scanning of said photosensitive medium, and said latent image is visualized. 15. The image forming apparatus according to claim 14, wherein the photosensitive medium is a photoconductive photoreceptor, the latent image is formed as an electrostatic latent image, visualized as a toner image, and the toner image is formed in a sheet shape. An image forming apparatus, which is finally carried on a recording medium according to (1).