JP5167880B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to tilt correction of an optical scanning line of an optical scanning device using a microscanner that swings a micromirror around a torsion bar axis and scans a light beam reflected on the mirror, a laser printer, a barcode reader, This invention is applicable to optical devices such as displays.

In conventional optical scanning devices, a polygon mirror is often used as an optical deflector that scans a light beam. The polygon mirror rotates at high speed and scans the light beam. However, in the image formation using the polygon mirror, it is necessary to rotate the polygon mirror at higher speed in order to achieve a higher resolution image and higher speed image formation. is there. However, to achieve high-speed rotation of the mirror, it is necessary to improve the durability of the bearing and take measures against heat generation and noise. Therefore, there is a limit to high-speed scanning using a polygon mirror.
Therefore, in recent years, an optical scanning device that scans a light beam has been proposed with a configuration that swings a micromirror (micromirror) using silicon micromachining technology. For example, in Patent Document 1, the micromirror is swung using a magnetic field generating means. In Patent Document 2, the micromirror is swung using electrostatic induction generating means. In Patent Document 3, the micromirror is swung by electrostatic attraction.

An optical scanning device using such silicon micromachining technology can scan faster than an optical scanning device using a polygon mirror, and the micromirror device can be realized with a size of several millimeters. The apparatus can be miniaturized.
However, even if any deflector such as a polygon mirror or a micro mirror is used, image degradation due to a displacement in the sub-scanning direction due to a variation in the shape of the deflector becomes a problem.
For example, the polygon mirror is composed of a plurality of deflecting mirror surfaces, but when each deflecting mirror surface is inclined with respect to the rotation center axis of the polygon mirror, so-called surface tilt occurs. As a result, the scanning position of the light beam on the optical scanning surface is deviated from the reference scanning position in the sub-scanning direction, and image quality is deteriorated.
As a method for correcting surface tilt, it is effective to arrange a pair of cylindrical lenses that act only in the sub-scanning direction before and after the deflector. For example, a cylindrical lens is arranged between the light source and the deflecting mirror to correct surface tilt.

Also in an optical scanning device using a micromirror device, the oscillating mirror itself is made of a thin substrate, so there is a drawback that the entire substrate is deformed in a direction perpendicular to the mirror swinging direction due to air resistance accompanying vibration. As a result, the problem that the focus position deviates from the surface to be scanned due to the reflection position of the light on the vibration mirror similarly occurs.
Furthermore, during operation of the optical scanning device, the light beam reference scanning position in the sub-scanning direction may vary due to fluctuations in the use environment of the scanning device, vibration, or changes over time. A so-called inclination of the optical scanning line is generated, which causes a larger image deterioration.
In order to solve such a problem, in Patent Document 4, the scanning imaging lens is rotated in the sub-scanning direction from the optical axis to correct the inclination of the scanning line to maintain the image quality.
JP 2002-78368 A JP-A-8-213320 Japanese Patent No. 30111144 JP 2006-259005 A

However, the accuracy of tilt correction by a mechanical method is limited. In addition, when a cylindrical lens or the like is arranged, the number of parts increases, and it becomes difficult to reduce the size of the optical system. As a result, it is difficult to reduce the size of the image forming apparatus. In addition, the cost of the apparatus cannot be reduced. In addition, since there are component dimensional errors and assembly dimensional errors in the surface tilt prevention mechanism, adjustment after assembly is required, and a dedicated adjustment jig may be required, and correction of the tilt of the optical scanning line is complicated. It required a complicated process.
The present invention has been made in view of the above circumstances, and detects the position of a light beam emitted from a light beam generating means having a matrix light emitting element structure in the sub-scanning direction and corrects the deviation of the light beam. Another object of the present invention is to provide an optical scanning device in which the deviation in the sub-scanning direction is corrected by a simple method other than the mechanical method by controlling the light beam generating means.

In order to solve the above-described problem, the invention described in claim 1 is directed to a light beam generating unit having a structure in which a plurality of light emitting elements are two-dimensionally arranged, and a light beam emitted from the light beam generating unit. and the light beam deflection means for deflecting a light beam detecting means for detecting an inclination of the scanning lines of the deflected the light beam by the light beam deflecting means to scan controls the light beam emitted from said light beam generating means And a light beam control unit, wherein the light beam control unit uses a light source used for light scanning based on an inclination of the scanning line detected by the light beam detection unit as the plurality of light emitting elements. The first light-emitting element is switched from the first light-emitting element to the second light-emitting element that is different from the first light-emitting element in the main scanning direction position and the sub-scanning direction position. And correcting the deviation in the main scanning direction position of the light beam generated by e.
According to a second aspect of the present invention, in the first aspect, the light beam control unit corrects the blinking start timing of the second light emitting element, thereby shifting the position of the light beam in the main scanning direction. It is characterized by correcting .
Further, an invention according to claim 3, in claim 1 or 2, wherein the light beam detecting means, passing of the light beam in the main scanning direction Ayamato, detect the position of the light beam in the sub-scanning direction characterized in that it.

According to a fourth aspect of the present invention, in the third aspect , the light beam control means measures a light beam position signal in the sub-scanning direction output from the light beam detection means, and outputs the light beam position signal to the light beam position signal. Computation means for calculating the inclination of the scanning line based on the above is provided .
Also, an invention according to claim 5, comprising a plurality of optical scanning apparatus according to any one of claims 1 to 4, wherein the light beam control means is selected from among a plurality of the optical scanning device The light source used for optical scanning for one optical scanning device is switched from the first light emitting element to the second light emitting element, and the scanning line of the light source used for optical scanning for the other optical scanning device is the second light emitting element. The light emitting element of the other optical scanning device is switched so as to match the scanning line .

According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the light source serving as a reference for optical scanning is set before the start of an image forming job.
Further, an invention according to claim 7, and an image forming unit, any one of claims 1 to 6 to form a latent image on the image forming unit by scanning a light beam in a predetermined area of the image forming unit one an optical scanning device according to claim, by developing the pre Kisenzo characterized an image forming apparatus having a developing means for forming a visible image, a.

  According to the present invention, optical scanning is performed using a light source having a matrix-shaped light emitting element structure that generates a plurality of light beams, and when a positional deviation (optical scanning tilt) in the sub-scanning direction occurs, the positional deviation is dealt with. Since the selected light source is selected to correct the optical scanning tilt, it is not necessary to install an optical scanning line tilt correcting member. Therefore, it is possible to reduce the number of parts, reduce the size of the optical scanning device and the image forming apparatus, and reduce the cost.

Hereinafter, embodiments of the present invention will be described in detail.
[Image forming apparatus]
An image forming apparatus to which the present invention is applied will be described. FIG. 1 is a schematic view of an image forming apparatus using an optical scanning device according to the present invention.
The image forming apparatus includes a developing unit 142, an optical scanning device 143, a charging unit 144, a cleaning unit 146, and a transfer unit 149 around the photoconductor 145. When the image forming apparatus control unit 153 that controls the operation of the entire image forming apparatus is instructed to start image formation, the photoconductor 145 rotates in the direction indicated by the arrow A, and the optical scanning apparatus 143 starts driving. A synchronization signal is generated, the photosensitive member 145 is charged by the charging means 144, and the light beam generator is synchronized with the synchronization signal corresponding to the image data input from the external input device (not shown) by the optical scanning device 143. A light beam is generated using 152 and a latent image is formed on the surface of the photoreceptor 145. Integer value image data of 0 to 255 representing the gradation value of the image corresponding to the density of the image data input from an input device (not shown) is input, and the beam emission time (width) is set corresponding to the input data. Is done. The set beam emission time setting data is supplied to a beam generator (not shown) of the light beam generator 152, and a signal generated by the beam generator is supplied to a beam driver (not shown) of the light beam generator 152. Then, an electric current is supplied to the laser diode which is a light emitting source, and the laser diode emits light to generate a light beam which forms a latent image on the surface of the photoconductor 145. A latent image is formed on the photoreceptor 145 by this light beam, and a visualized image is obtained by the developing means 142 using an image visualization agent.
The paper stored in the paper storage unit 140 is fed by the paper feeding unit 141, the paper conveyance timing and the writing timing are matched by the registration unit 151, and the visible image by the image visualization agent is transferred to a predetermined position by the transfer unit 149. Make it possible. The actual image transferred by the image visualization agent transferred onto the paper is fixed by the fixing unit 147, and the input image data is visualized and fixed on the paper.

[Optical scanning device]
The optical scanning device 143 will be described. FIG. 2 is a schematic diagram of an optical scanning device 143 according to the present invention. As shown in FIG. 2, the optical scanning device 143 includes a deflecting mirror 40, a light beam generating unit 44, a collimating lens 45, and an fθ lens 63 in the optical system housing 50, and a light beam on the main scanning line of the image carrier 60. Detection means 49 is provided.
The light beam emitted from the light beam generating means 44 capable of generating a plurality of beams passes through a collimating lens 45 that corrects the emitted beam to parallel light, and is scanned by the deflection mirror 40 in the main scanning direction. . The beam reflected by the deflecting mirror forms an image on the surface of the image carrier 60 through the fθ lens. The light beam formed on the image carrier 60 performs reciprocal scanning in the main scanning direction. A light beam detecting means 49 is disposed on the optical scanning line. The light beam detecting means 49 includes a light beam passage detector 47 that detects the passage of the beam in the main scanning direction and a sub-scanning that detects the beam position in the sub-scanning direction. And a directional position detector 48. In the light beam scanning by the deflection mirror 40 of the present optical scanning device, there is a conversion point in the optical scanning direction, unlike the conventional rotary polygon mirror. Therefore, the light beam 62 reciprocates on the image carrier 60.
While the light beam scans the image carrier 60, a light beam controller 300 described later blinks the light beam at a predetermined interval, thereby forming an image on the image carrier 60. As a factor that affects the image quality of a formed image, it is known that the positional accuracy of pixels formed by causing the image carrier 60 to scan with a light beam is important. In general, it is said that fluctuations in adjacent pixel positions must be kept within ½ pixel in order to prevent image degradation. In the present invention, image degradation is prevented by selecting the light emitting element of the light beam generating means 44 based on the light beam detection result from the light beam detecting means 49. The relationship between image quality deterioration and pixel position fluctuation, and a method for preventing image quality deterioration will be described later.

[Deflection mirror]
Here, the deflection mirror 40 applied to the present invention will be described with reference to FIG.
FIG. 3 is a perspective view of a deflection mirror 40a which is an embodiment of the deflection mirror 40 applied to the present invention.
The deflection mirror 40 a includes a support substrate 1 made of silicon and a movable plate 7, and the support member 1 supports the central portion of two opposite end portions of the movable plate 7 on the support substrate 1. A movable electrode 4 is provided on two opposing end surfaces of the movable plate 7 where the support member 2 is not disposed, and a fixed electrode 3 is provided on the end surface of the support substrate 1 at a position facing the movable electrode 4.
A gap of, for example, 5 μm is provided between the movable electrode 4 and the fixed electrode 3 opposed to the movable electrode 4. By applying a voltage between these electrodes, electrostatic attraction works between the electrodes, and the movable plate 7 The end face is attracted to the fixed electrode 3, and the movable plate 7 swings.

The operation of the deflection mirror 40a configured as described above will be described with reference to FIG.
FIG. 4 is a diagram for explaining the operation of the deflection mirror. In FIG. 4, the movable electrode 4 attached to the movable plate 7 is drawn out to the support substrate 1 and grounded through a pad (not shown). When the positional relationship between the fixed electrode 3 and the movable electrode 4 is in the state shown in FIG. 4A, when a voltage of, for example, 30 V is applied to the fixed electrode 3, an electrostatic force acting between the fixed electrode 3 and the movable electrode 4 and a beam ( Due to the torsional rigidity of the support member 2), the movable plate 7 swings clockwise in the figure. As shown in FIG. 4B, when the voltage application to the fixed electrode 3 is turned off when the movable plate 7 reaches the horizontal position with respect to the support substrate 1, the movable plate 7 is rotated clockwise by the moment of inertia. Further shakes. Finally, as shown in FIG. 4 (c), it swings to a position where the moment of inertia and the torsional rigidity of the beam (supporting member 2) are balanced. When the maximum deflection angle is reached, the movable plate 7 temporarily stops, and then starts to shake in the direction opposite to the direction in which the movable plate 7 has shaken. In FIG. 4, it starts to swing counterclockwise. When the voltage is applied again to the fixed electrode 3 at an appropriate time after starting to oscillate counterclockwise, the movable plate 7 is caused by the electrostatic force acting between the fixed electrode 3 and the movable electrode 4 and the torsional rigidity of the beam (support member 2). Shake counterclockwise in the figure. When the voltage application to the fixed electrode 3 is turned off when the movable plate reaches the horizontal position with respect to the support substrate 1 again, the movable plate 7 further swings counterclockwise due to the moment of inertia. Finally, as shown in FIG. 4 (a), it swings to a position where the moment of inertia and the torsional rigidity of the beam (supporting member 2) are balanced.
By adjusting the voltage application frequency to the fixed electrode 3 to the resonance frequency of the movable plate, the movable plate 7 can be swung with a large deflection angle.

  FIG. 5 is a perspective view of a deflection mirror 40b, which is another embodiment of the deflection mirror 40. FIG. Two opposing ends of the movable plate 7 where the support member 2 is not disposed have a comb shape, and the end of the support substrate 1 facing the comb-shaped portion of the movable plate 7 also has a comb shape. ing. Each comb-tooth shaped portion has a shape that meshes with a small gap therebetween. A movable electrode 4 is provided on the end surface of the comb-shaped portion of the movable plate 7, and a fixed electrode 3 is provided on the end surface of the comb-shaped portion of the support substrate 1. This comb tooth shape acts as a drive electrode. By making the electrodes into a comb-like shape in this way, the electrode area can be increased, so that the driving torque can be further increased and the deflection angle of the movable plate 7 can be further increased. In this way, when the light beam is irradiated onto the reflecting surface 5 of the movable plate 7 that swings, the incident light can be deflected by the reflecting surface 5 by the swing of the movable plate 7.

FIG. 6 is a diagram for explaining the oscillation frequency of the movable plate 7. In this figure, the support member 2 has a torsion beam structure. The movable plate 7 supported by the support member 2 can rotate and swing around the support member 2. The oscillation frequency fy of the movable plate 7 is approximated by the following formula (1).
fy = 1 / 2π√ (Ky / Iy)
(1)
However, fy: resonance frequency of the movable plate 7, Iy: moment of inertia, Ky: spring constant.
The spring constant Ky is given by the following equation (2), assuming that the beam width is a, the beam height is b, and the beam length is Ly.
Ky = (Jp × G) / Ly,
Jp = 0.141 × a × b ^ 3,
G = Ey / (2 (1 + ι)),
(2)
Where Ey: Young's modulus and ι: Poisson's ratio.
Further, the inertia moment Iy is given by the following equation (3), assuming that the movable plate 7 has a lateral width d, a length e, and a thickness c.
Iy = My × (e ^ 2 + c ^ 2) / 12,
My = ρ (d × e × c)
(3)
From the above equations (1) to (3), it can be seen that the resonance frequency fy is determined by the shapes of the support member 2 and the movable plate 7.

[Light beam generation means]
The light beam generating means 44 will be described. The light beam generating means 44 includes a surface emitting laser 44a capable of generating a plurality of light beams. FIG. 7 is an example of a surface emitting laser, where (a) is a schematic diagram of the surface emitting laser, and (b) is a diagram illustrating a light emitting element provided in the surface emitting laser.
The surface emitting laser of FIG. 7 has a matrix light emitting element structure in which a plurality of light emitting regions (light emitting points) that can be independently modulated are arranged in a two-dimensional array. In the case of this surface emitting laser, it is constituted by an optical element structure having a resolution of 1200 dpi, and an image of 600 dpi can be formed by using this plurality of light sources. In addition, it is possible to configure a multi-beam scanning device that scans a plurality of light sources and simultaneously scans a plurality of scanning lines by one scanning. For example, if three light sources arranged in the sub-scanning direction are selected and the light sources are blinked in time corresponding to the image data while scanning in the main scanning direction, light beam scanning in the main scanning direction is performed once in the sub-scanning direction. It is possible to form an image at three sub-scanning positions.

As shown in FIG. 7B, this surface emitting laser has a total of 40 light emitting points including 10 (10 columns) light emitting points in the main scanning direction and 4 light emitting points (4 rows) in the sub scanning direction. It has. In the figure, they are called first light source, second light source,. In the figure, the 14th light source is the reference light source. The spacing between the columns is L = 21.1 μm, and the spacing between the rows is D = 21.1 μm, but the light sources having adjacent numbers are shifted by Δd = D / k in the sub-scanning direction. Here, k is the number of light emitting points in the main scanning direction. In the example of FIG. 7, since k = 10, Δd = D / k = 2.11 μm. Therefore, this surface emitting laser can correct the position fluctuation of the light beam in the sub-scanning direction in units of 1/10 pixel.
That is, by using such a surface emitting laser, a setting is made to reciprocately scan the light beam at the main scanning reference position FSB using an arbitrary nth light source selected from a plurality of light sources of the surface emitting laser. Even if the sub-scanning direction position detector 48 detects that the position of the light beam fluctuates in the sub-scanning direction from the main scanning reference position FSB, the m-th light source capable of correcting the fluctuation By changing to the setting for reciprocating scanning using, the light beam can be reciprocated at the main scanning reference position FSB.
At this time, since the nth light source position and the mth light source position are different, it is necessary to correct the blinking start timing for image formation, which will be described later.
As described above, even if fluctuations in the main scanning reference position FSB (inclination of the main scanning reference position) occur, deterioration in image quality can be prevented by the above configuration.

Here, the relationship between image quality degradation and pixel position fluctuation will be described.
In general, it is said that the threshold value of whether or not it is recognized that the image is deteriorated is determined by whether or not the adjacent pixel position varies more than 1/2 pixel. That is, the positional fluctuation Δd allowed in order not to deteriorate the image quality is
1/4 pixel <Δd <1/2 pixel is a required value,
1/8 pixel <Δd <1/4 pixel is the expected value,
1/16 pixel <Δd <1/8 pixel is the best value.
Therefore, if the interval in the sub-scanning direction of the matrix light emitting element is (1 / k) pixels, 1/4 / (1 / k) <1/2 is an essential value for (1 / k), and 1/8 pixel. <(1 / k) <1/4 pixel is an expected value, and if 1/16 <(1 / k) <1/8 can be realized, it is effective in reducing image quality degradation.
In the example of FIG. 7, the position in the sub-scanning direction can be controlled in units of 1/10 pixels, and the best value requirement is satisfied, so that an effect of suppressing image deterioration can be expected.

[Light beam detection means]
The light beam detecting means 49 will be described with reference to FIGS. As described above, the light beam detector 49 includes the light beam passage detector 47 that detects the passage of the beam in the main scanning direction and the sub-scanning direction position detector 48 that detects the beam position in the sub-scanning direction. .
First, the sub-scanning direction position detector 48 will be described. 8A and 8B are diagrams for explaining the sub-scanning direction position detector 48. FIG. 8A is a diagram for explaining the photodetector and the light detection position. FIG. 8B is a diagram showing the relationship between the light detection position and the photocurrent. It is. The sub-scanning direction position detector 48 is means for detecting the position in the sub-scanning direction when the light beam scans in the main scanning direction. The sub-scanning direction position detector 48 includes a photodetector, and can detect a photocurrent generated by the light incident position of the photodetector. As shown in FIG. 8B, there is a predetermined relationship between the light incident position and the generated photocurrent. That is, it is possible to know the light incident position by measuring the photocurrent.

  Assume that the main scanning reference position FSB is set to a light source that reciprocally scans the light detection position 0 shown in FIG. 8A among a plurality of light sources included in the surface emitting laser 44a. However, if the light beam reciprocating scanning position fluctuates in the sub-scanning direction for some reason, and the photocurrent is detected to be about 70% by the sub-scanning direction position detector 48, it is understood that the position is the light detection position + 1. . Therefore, the direction of fluctuation and the amount of fluctuation can be known. Based on this information, a new light source capable of optically scanning the main scanning reference position FSB is selected from a plurality of light sources provided in the surface emitting laser 44a. When an image is formed on the image carrier 60 using the newly selected light source in this manner, the position of the surface emitting laser 44a in the main scanning direction is determined by the initially selected light source and the newly selected light source. If they are different from each other, the timing for starting image formation is shifted, so the image formation timing is adjusted based on the light beam detection information from the light beam passage detector 47.

The light beam passage detector 47 will be described. 9A and 9B are diagrams for explaining the light beam passage detector 47. FIG. 9A is a diagram showing an outline of the detector, and FIG. 9B is a diagram showing an outline of the detection circuit.
As shown in (a), the light beam passage detector 47 detects the light beam incident on the light receiving window. For detection of the light beam, it is preferable to use a photodiode or the like with good response characteristics. The light beam incident on the light receiving window generates a photoelectromotive force by a photodiode (not shown), is input to the circuit shown in (b), is amplified by an operational amplifier, and is output from Vo as a voltage change. Then, as shown in FIG. 17, the flashing start timing of the light emitting element is obtained according to the time Ta when the light beam reciprocates between the first reference point Lb1 and the forward direction end portion Le1, and the light emitting element is caused to emit light at that timing. . Details will be described later.
As described above, the light beam detecting means 49 is composed of two light receiving elements, that is, the light beam passage detector 47 and the sub-scanning direction position detector 48, so that the positional deviation in the sub-scanning direction can be calculated in a timely manner. The formation timing can be controlled, and image deterioration can be prevented.

[Optical scanning device control means]
The optical scanning control device that controls the optical scanning device 143 will be described based on the control system block diagram of FIG.
The light scanning control device 300 controls the light beam generated by the light beam generation means 44 and the light beam deflected by the deflecting mirror 40 so as to blink the light beam in the specific light scanning range Lx while reciprocating scanning. A light scanning mechanism 301 that causes the light beam to enter and deflects and emits the light beam by the deflection mirror 40, a light beam detection / calculation unit 304 that detects the passage timing and sub-scanning position of the light beam, and a microphone processor (MPU). ), A central control arithmetic processing unit 303 including a read only memory (ROM), a random access memory (RAM), and the like.

The sub-scanning position detector 48 detects the sub-scanning position, and the position detection signal processing unit 252 performs signal calculation processing so that the sub-scanning position can be recognized with an accuracy of 1/10 line, and relates to the sub-scanning position. Various arithmetic circuits 253 calculate the direction of change and the amount of change from the reference position of the sub-scanning direction position detector 48. For example, if the reference position of the sub-scanning direction position detector 48 is mechanically designed in FIG. 8b and the part where the photocurrent is 50% at the light detection position 0, the photoelectric sensor detected by the sub-scanning direction position detector 48 is used. The flow rate and the reference position. From the comparison with the photocurrent 50%, the fluctuation direction and the fluctuation amount from the reference position can be calculated.
The sub-scanning direction position detectors 48 shown in FIG. 2 are arranged on the left and right on the optical scanning line, and can detect the position in the sub-scanning direction, thereby allowing the optical scanning line to tilt, tilt direction, and lateral displacement. A quantity difference or the like can be detected and calculated.

[First embodiment]
An image quality deterioration prevention method according to the first embodiment by the optical scanning device 143 having the above-described configuration will be described with reference to FIG.
In the surface emitting laser 44a of FIG. 7A, the 14th light source is set as the reference light source for scanning the main scanning reference position FSB, and the setting is made to scan the 3rd light source of the 4th light source, the 14th light source, and the 24th light source at a time. Suppose that was done. At this time, as shown in FIG. 11, for example, it is assumed that the deflection mirror 40 is tilted, and an image 71 that varies in the sub-scanning direction is formed on the image carrier 60. When the displacement Δp with respect to the main scanning reference position FSB is obtained from the measurement result by the sub-scanning direction position detector 48, the displacement Δp is corrected by changing the reference light source from the 14th light source to another light source. To do. As a specific example, when the fluctuation on the image carrier 60 is Δp = (1 + 1/10) pixels in the sub-scanning direction, the reference light source for scanning the main scanning reference position FSB is sub-scanned with respect to the 14th light source. By setting the 25th light source separated by Δp = (1 + 1/10) in the scanning direction, the light source for scanning the main scanning reference position FSB on the image carrier 60 can be reset. This setting is performed by the light beam control unit 300. By this resetting, image formation is performed by newly scanning three light sources of the 15th light source, the 25th light source, and the 35th light source.

Here, since the light source position before the change and the light source position after the change are different in the main scanning direction, it is necessary to correct the blinking start timing for image formation. This will be described.
FIG. 12 is a diagram showing the scanning of the light beam on the image carrier 60 and the swing waveform of the deflection mirror 40. The light beam emitted from the light beam generating means 44 is deflected and emitted by being incident on the deflecting mirror 40 and reciprocally scans on the image carrier 60. The light beam reciprocally scans the entire scanning region La (between the forward direction end portion Le1 and the backward direction end portion Le2), and is controlled to blink in the specific light scanning range Lx, so that a latent image is formed on the image carrier 60. Written. A trajectory line on which the light beam reciprocates is set as the main scanning reference position FSB.
In FIG. 12, the forward direction end portion (right end portion in the figure) of the image carrier 60 and the forward direction end portion Le1, and the backward direction end portion (left end portion in the drawing) of the image carrier 60 and the return path. The light beam detection means 49 is respectively arranged at an arbitrary position between the direction end portion Le2. The light beam passage detector 47 detects the passage of the first reference point Lb1 and the second reference point Lb2 in the main scanning direction of the light beam. Whether the sub-scanning direction position detector 48 performs reciprocal scanning at the main scanning reference position FSB of the light beam when the light beam passes through the first sub-scanning monitoring point Lc1 and the second sub-scanning monitoring point Lc2. Whether or not the position deviation from the main scanning reference position FSB in the sub-scanning direction is detected.

  The blinking control of the light beam and the image formation timing on the image carrier 60 will be described. When scanning in the forward direction by the light beam is started, the passage of the first reference point Lb1 is detected by the light beam passage detector 47 arranged on the right side in the drawing. The light beam returns at the forward direction end portion Le1 and starts scanning in the backward direction. Then, when the light beam passes through the first reference point Lb1 by scanning in the backward direction, the light beam passage detector 47 arranged on the right side in the drawing detects. The time Ta from when the light beam passes through the first reference point Lb1 until it passes through the first reference point Lb1 at the outward direction end Le1 is measured by the optical signal detection / calculation unit 304 provided in the optical scanning control device. Is done. Based on the measured light beam scanning time Ta, the time from the passage through the first reference point Lb1 to the start of blinking is calculated, blinking according to the formed image data is started, and image formation in the backward direction is started. Is done. When scanning in the backward direction is completed, as in the forward direction, the time Td from when the light beam passes the second reference point Lb2 and turns back at the backward direction end portion Le2 to pass through the second reference point Lb2 is the optical signal detection / The time until the light beam starts blinking is calculated based on the light beam scanning time Td measured by the arithmetic unit 304, blinking according to the formed image data is started, and image formation in the forward direction is performed. Thus, the image formation on the image carrier 60 is adjusted by the scanning time from the first reference point Lb1 or the second reference point Lb2.

Thus, when an image is formed on the image carrier 60 during the reciprocation of the light beam, the number of blinks in the specific light scanning range Lx is calculated from the pixel density formed in the specific scanning range Lx as follows. For example, if the pixel density is Mdpi (dot / inch), the total number of pixels is L × M.
As described above, the present embodiment includes the sub-scanning direction position detector 48 that detects the inclination of the optical scanning line in the sub-scanning direction based on the detection information from the light beam detecting means 49. Even if a positional deviation in the scanning direction occurs, image quality deterioration can be prevented by performing image formation control on the image carrier 60 corresponding to the positional deviation. Further, since the light source is a plurality of light sources having a matrix-shaped light emitting element structure that generates a plurality of light beams, even if the light beam is displaced in the sub-scanning direction, a light source corresponding to the displacement is selected. Thus, it is possible to correct the optical scanning inclination of the light beam and to control the image formation on the image carrier corresponding to the positional deviation.

[Second Embodiment]
A second embodiment of the present invention will be described. In the second embodiment, an image quality deterioration prevention method when the optical scanning line is inclined will be described.
FIG. 13 is a view showing a state in which the optical system housing 50 is tilted. The optical system housing 50 is changed in the direction of arrow C in the figure, and the optical scanning line is inclined and scanned with respect to the main scanning reference position FSB. In such a state, the image formed on the image carrier 60 is deformed, or the shape of the beam spot formed on the image carrier 60 is deformed due to the inclination, thereby causing image unevenness.
As described above, when the optical beam reference scanning position in the sub-scanning direction changes due to a change in usage environment of the optical scanning device 143 or a change with time during operation of the optical scanning device 143, correction is conventionally performed by a mechanical method. Had gone. For example, when an influence due to a temperature rise, which is one of use environment fluctuations, occurs, the optical scanning is temporarily stopped and the temperature is restored to a steady state, or the optical system housing 50 is configured. Attempted to correct the position of the optical scanning mirror.
In this embodiment, the inclination of the scanning line is corrected by sequentially changing the light emitting elements of the surface emitting laser 44a without using a mechanical method. In the following, for the sake of convenience, the inclination correction of the scanning line emitted from one reference light source will be described. However, the same correction can be made in multi-beam scanning.

FIG. 14 is a diagram illustrating an image quality deterioration prevention method according to the second embodiment. In the drawing, a portion surrounded by a square frame indicates the surface emitting laser 44a and its light emitting element. In the following description, it is assumed that the sixth light source is a reference light source.
As shown in FIG. 14, the optical scanning line SLθ of the reference light source is inclined by θ with respect to the main scanning reference position FSB. That is, when light beam scanning is performed, the reference light source moves in the direction of arrow D with an angle θ in the main scanning direction with respect to the main scanning reference position FSB, and each pixel is formed on SLθ. For this reason, the image on the image carrier 60 is formed in a deformed or distorted state.
However, even when the reference light source is scanning on the inclined optical scanning line SLθ, the light source corresponding to the determined pixel formation position on the main scanning reference position FSB on the image carrier 60 is There is at least one in the surface emitting laser 44a. A pixel is formed on the main scanning reference position FSB by emitting the corresponding light source.

FIGS. 15A to 15D are diagrams illustrating the flow of pixel formation from the nth pixel to the (n + 3) th pixel. In (a), since the nth pixel corresponds to the first light source, the first light source is caused to emit light to form a pixel. Scanning proceeds by one pixel. In (b), since the (n + 1) th pixel corresponds to the second light source, the second light source emits light to form a pixel. Scanning further proceeds by one pixel. In (c), since the (n + 2) -th pixel corresponds to the third light source, the third light source emits light to form a pixel. Scanning further proceeds by one pixel. In (d), since the (n + 3) -th pixel corresponds to the fourth light source, the fourth light source emits light to form a pixel.
In this manner, the light source of the surface emitting laser 44a corresponding to the determined pixel formation position on the main scanning reference position FSB on the image carrier 60 is sequentially selected to emit light to form pixels, thereby forming the image carrier. The latent image forming position to 60 can be controlled.

[Calculation of tilt angle θ]
Here, an example of a method for calculating the inclination angle θ that the optical scanning line SLθ of the reference light source has with respect to the main scanning reference position FSB will be described.
FIG. 16 is a diagram illustrating a state in which the optical scanning line SLθ is inclined with respect to the main scanning reference position FSB on the image carrier 60. The sub-scanning direction position detector 48 detects the amount of displacement of the light beam with respect to the main scanning reference position FSB at the first sub-scanning monitoring point Lc1 as + Δp1, and the main scanning reference position at the second sub-scanning monitoring point Lc2 It is assumed that the amount of displacement of the light beam with respect to the FSB is detected as -Δp2. At this time, the displacement Δpa of the light beam between Lc1 and Lc2 is given by Δpa = | + Δp1 − (− Δp2) |. The inclination angle θ is obtained from Δpa and the distance between Lc1 and Lc2. Further, the intersection position between the main scanning reference position FSB and the inclined optical scanning line SLθ is obtained from the relationship between Δp1 and Δp2.

The displacement data of the light beam from the sub-scanning direction position detector 48 is input to the position detection signal processing unit 252 of the optical signal detection / calculation unit 304 shown in FIG. Then, numerical calculation processing such as detection signal average value processing, integral value processing, differential value processing, and fluctuation frequency analysis processing is performed. The light source selection means of the light beam control unit 300 varies based on numerical values such as the intersection position relationship between the main scanning reference position FSB and the inclined light scanning line SLθ obtained by such numerical calculation processing and the inclination angle θ. Select a light source that can be modified. Note that the correction of fluctuations from the main scanning reference position FSB of the beam scanning by the reference light source is performed by a method based on the feedback control theory, and appropriate light source selection can be realized by high-speed calculation processing.
As described above, since the calculation means for calculating the inclination amount and the inclination direction of the scanning line based on the position detection signal of the light beam output from the light beam detection means 49 is provided, more appropriate image deterioration prevention can be achieved. Can be realized. Further, since the inclination of the optical scanning line is corrected based on the calculation result, more appropriate image deterioration prevention can be realized.

[Third embodiment]
The swing angle of the oscillating mirror as described above is generally about 10 ° or less, and it is difficult to obtain a scanning angle up to about 40 ° of the light beam swing angle by the polygon mirror. For this reason, in the image formation using the optical scanning device using the oscillating mirror, it is necessary to increase the optical path length in order to secure the scanning width, and there is a disadvantage that the size of the optical scanning device increases. It was.
The oscillating mirror was used to ensure the same image formation recording width as the polygon mirror while taking advantage of the downsizing, high speed, and power saving that are the advantages of the optical scanning device using the oscillating mirror. A method for realizing image formation by arranging a plurality of optical scanning devices adjacent to each other has been proposed. However, when performing image formation by arranging the optical scanning devices adjacent to each other independently, if the optical scanning phase of each optical scanning device and the optical scanning trajectory do not match each other, the positional deviation of the start position, In addition, a change in the recording width in the main scanning direction due to a mismatch in scanning cycle or an error in the sub-scanning line pitch may be accumulated, and there is a possibility that the seams between adjacent scanning lines are shifted.

In the present invention, the optical scanning device according to the first and second embodiments is modularized so that the fluctuation of the optical scanning line can be corrected for each module.
The optical scanning module will be described. FIG. 17 is a diagram showing an outline of an optical scanning module 203 obtained by modularizing the optical scanning device of the present invention. The optical scanning module 203 includes a light beam generating unit 44 that generates a light beam, a deflection mirror 40 that deflects the light beam, a conversion fθ lens 207 that converts equiangular scanning into constant speed scanning, and a conversion fθ lens 208. It has. Although not shown, this module reflects a mirror that reflects a light beam outside the specific light scanning range Lx out of the light beam that has passed through the conversion fθ lens 208, and a light beam detection means that detects the reflected light beam. 49, and fluctuation correction of the light beam is possible for each module.

FIG. 18 is a diagram showing a state in which a plurality of optical scanning modules 203 are arranged adjacent to each other in the long axis direction of a photoconductor that is an image carrier. In this figure, four optical scanning modules 203 are arranged for a single photoconductor.
Each optical scanning module 203 can optically scan an arbitrary range by dividing the surface of the photoreceptor 211. The light beam emitted from the light beam generating unit 44 is deflected by the deflection mirror 40 which is a light beam deflecting unit, and is scanned in the main scanning direction which is the major axis direction of the photosensitive member 211. Conversion fθ lenses 207 and 208 for converting equiangular scanning into constant speed scanning and an optical path changing mirror 209 are disposed on the scanning optical path, and a minute laser beam spot 212 is imaged on the surface of the photosensitive member 211. The minute laser beam spot 212 is formed at the main scanning reference position FSB, and the main scanning reference position FSB of each optical scanning module 203 needs to match.
However, FIG. 18 shows a state in which the main scanning reference position FSB does not coincide with the optical scanning line SL tilted with respect to the main scanning reference position FSB of each optical scanning module 203. In such a state, a deviation in the image formation start position, a change in the recording width in the main scanning direction due to a mismatch in scanning cycle, or an error in the sub-scanning line pitch is accumulated, and a seam between adjacent scanning lines is shifted. , Image degradation is significantly increased. In order to improve such a problem, the fluctuation of the optical scanning line SL is corrected for each optical scanning module 203 by the method described in the first embodiment and the second embodiment.

First, an arbitrary module is selected from the plurality of optical scanning modules 203, the fluctuation of the optical scanning line is corrected for this module, and a light source for scanning the main scanning reference position FSB is set. Then, the optical scanning lines of the other optical scanning modules 203 are corrected in accordance with the corrected optical scanning lines of the optical scanning module 203.
As described above, when a plurality of optical scanning devices are provided, the tilt of the changed scanning line is corrected so that the scanning line of another optical scanning device is aligned with the scanning line of an arbitrary optical scanning device. Thus, it is possible to prevent image degradation when the optical apparatus is configured by a plurality of optical devices.

[Fourth embodiment]
The variation correction timing of the optical scanning line SL described so far will be described.
The arithmetic circuits 253 related to the sub-scanning position of the control system block shown in FIG. 10 perform light beam scanning a plurality of times every time image formation on the image carrier 60 is started, and average the detection results of the plurality of light beams. Based on the obtained data, a light source capable of scanning the main scanning reference position FSB is determined. Thereafter, image formation is performed. This operation is performed every time a series of jobs is completed and a new job is started. The selection information of the selected light source for each job is also stored in the RAM 233 of the control block and managed as operation information of the image forming apparatus.
Thus, by setting the reference light source for image formation before the start of the image forming job, the main scanning reference position FSB can be determined for each new job, and the influence of past image deterioration can be eliminated.

1 is a schematic view of an image forming apparatus using an optical scanning device according to the present invention. It is the schematic of the optical scanning device concerning this invention. It is a perspective view of one Embodiment of the deflection | deviation mirror applied to this invention. It is a figure explaining operation | movement of a deflection | deviation mirror. It is a perspective view of other embodiment of the deflection | deviation mirror applied to this invention. It is a figure explaining the rocking | fluctuation frequency of a movable plate. It is an example of a surface emitting laser, (a) is the schematic of a surface emitting laser, (b) is explanatory drawing of the light emitting element with which a surface emitting laser is equipped. It is a figure explaining a subscanning direction position detector, (a) is explanatory drawing of a photodetector and a photon detection position, (b) is a figure which shows the relationship between a photon detection position and a photocurrent. It is a figure explaining a light beam passage detector, (a) is a schematic diagram of a detector, (b) is a figure showing an outline of a detection circuit. It is a control system block diagram of the optical scanning control apparatus which controls an optical scanning apparatus. It is a figure explaining the image quality degradation prevention method by an optical scanning device. It is a figure which shows the scanning of the light beam on an image carrier, and the rocking | fluctuation waveform of a deflection | deviation mirror. It is a figure which shows the state which the optical system housing inclined. It is a figure explaining the image quality degradation prevention method which concerns on 2nd embodiment. It is a figure which shows the flow of pixel formation from the n-th pixel to the n + 3 pixel. It is a figure which shows a mode that the optical scanning line inclines with respect to the main scanning reference position. It is the schematic of an optical scanning module. It is a figure which shows a mode that the some optical scanning module 203 was arrange | positioned adjacent to the longitudinal direction of the photoconductor which is an image security body.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Support substrate, 2 ... Support member, 3 ... Fixed electrode, 4 ... Movable electrode, 5 ... Reflecting surface, 7 ... Movable plate, 40, 40a, 40b ... Deflection mirror, 44 ... Light beam generating means, 44a ... Surface emission Laser, 45 ... collimating lens, 47 ... light beam passage detector, 48 ... sub-scanning direction position detector, 49 ... light beam detection means, 50 ... optical system housing, 60 ... image carrier, 62 ... light beam, 63 ... Lens, 71 ... Image, 140 ... Paper storage unit, 141 ... Feeding means, 142 ... Developing means, 143 ... Optical scanning device, 144 ... Charging means, 145 ... Photoconductor, 146 ... Cleaning means, 147 ... Fixing means, 149 DESCRIPTION OF SYMBOLS Transfer means 151 ... Registration part 152 ... Light beam generator 153 ... Image forming apparatus control part 203 ... Optical scanning module 207 ... f (theta) lens 208 ... f (theta) lens 209 ... Optical path Change mirror, 211 ... photosensitive member, 212 ... micro laser beam spot, 233 ... RAM, 252 ... position detection signal processing unit, 253 ... various arithmetic circuits, 300 ... light beam control unit, 301 ... light scanning mechanism, 303 ... central control Arithmetic processing unit, 304... Arithmetic unit

Claims (7)

A light beam generating means in which a plurality of light emitting elements having a two-dimensional arrangement structure, a light beam deflecting means for deflecting the light beam emitted from said light beam generating means, said deflected by said light beam deflecting means In an optical scanning device comprising: a light beam detecting means for detecting a tilt of a scanning line of a light beam; and a light beam control means for controlling the scanning of the light beam emitted from the light beam generating means.
The light beam control means, based on the inclination of the scanning line detected by the light beam detection means, makes a light source used for optical scanning from the first light emitting element of the plurality of light emitting elements to the first light emitting element. Switching to a second light emitting element having a different main scanning direction position and sub-scanning direction position from the light emitting element, and correcting a deviation of the position of the light beam in the main scanning direction caused by the switching to the second light emitting element. An optical scanning device characterized by the above. 2. The optical scanning device according to claim 1, wherein the light beam control unit corrects a deviation of a position of the light beam in a main scanning direction by correcting a blinking start timing of the second light emitting element. 3. . It said light beam detecting means, a main passage of the light beam scanning direction Ayamato optical scanning device according to claim 1 or 2 and the position of the light beam in the sub-scanning direction, and detecting the to. The light beam control means includes a calculation means for measuring a light beam position signal in the sub-scanning direction output from the light beam detection means and calculating an inclination of the scanning line based on the light beam position signal. The optical scanning device according to claim 3 . A plurality of optical scanning apparatus according to any one of claims 1 to 4, wherein the light beam control means, an optical scanning device selected from among a plurality of the optical scanning device a light source used for the optical scanning While switching from the first light emitting element to the second light emitting element, the other optical scanning is performed so that the scanning line of the light source used for optical scanning in the other optical scanning device matches the scanning line of the second light emitting element. An optical scanning device, wherein the light emitting element of the device is switched . The optical scanning device according to any one of claims 1 to 5, characterized in that setting the light source as a reference optical scanning before the start of the image forming job. An image forming unit, an optical scanning apparatus according to any one of claims 1 to 6 in a predetermined area of the image forming unit by scanning light beam to form a latent image on the image forming section, prior Symbol An image forming apparatus comprising: a developing unit that develops a latent image to form a visualized image.

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