JP4689462B2 - Optical scanning device and image forming device - Google Patents

Description

The present invention relates to an optical scanning device that optically scans a surface to be scanned, and an image forming apparatus such as a copying machine, a printer, a facsimile, or a plotter having the optical scanning device.
The present invention can also be applied to an optical scanning bar code reader, an in-vehicle laser radar device, and the like.

In a conventional optical scanning device, a polygon mirror or a galvanometer mirror is used as a deflector that scans a light beam. In order to achieve a higher resolution image and high-speed printing, this rotation must be further increased, and a bearing is used. Durability, heat generation due to wind damage, and noise are issues, and there is a limit to high-speed scanning.
On the other hand, in recent years, research on a deflection device using silicon micromachining has been promoted, and as disclosed in Patent Document 1 and Patent Document 2, an oscillating mirror and a torsion beam pivotally supported by a Si substrate are integrated. The formed method is proposed.

According to this method, there is an advantage that the mirror surface size can be reduced and the size can be reduced, and since reciprocal vibration is performed using resonance, high speed operation is possible but low noise and low power consumption are possible.
Furthermore, since the vibration is low and there is almost no heat generation, the housing that houses the optical scanning device can be thinned, and even if a low-cost resin molding material with a low glass fiber content is used, the image quality is affected. There is also an advantage that it is difficult.
Patent Documents 3 and 4 disclose examples in which a vibrating mirror is provided instead of a polygon mirror.

In general, assuming a simple plate-like oscillating mirror as shown in FIG. 19, the dimensions of the oscillating mirror are the width d in the direction parallel to the rotation axis, the width 2r in the direction perpendicular to the rotation axis, the thickness t, and the torsion. If the dimensions of the beam are length h and width a, the density ρ of Si and the material constant G are used.
Moment of inertia I = (4ρrdt / 3) · r2
Spring constant K = (G / 2h) · {at (a2 + t2) / 12}
The resonance frequency f0 is
f0 = (1 / 2π) · √ (K / I) = (1 / 2π) · √ {Gat (a2 + t2) / 24LI}
It becomes.
Here, since the length L of the torsion beam and the deflection angle θ0 are in a substantially proportional relationship, the deflection angle θ is θ0 = κ / I · f02 κ is a constant (1)
The resonance frequency f0 changes depending on the spring constant K of the torsion beam, and the deflection angle θ also changes accordingly.

By the way, with respect to the peripheral speed υ and area E (= 2rd) of the oscillating mirror, if the density of air is η, the viscous resistance of air P = C · ηυ ^ 2 · E ^ 3 C is constant against the rotation of the oscillating mirror. Work.
On the other hand, the relationship between the vibration torque T and the swing angle θ0 is
θ0 = κ '· T / K κ' is a constant (2)
Therefore, in order to keep the deflection angle θ stable, the applied current may be adjusted so as to generate the rotational torque T corresponding to the change in the spring constant K of the torsion beam and the air resistance.

As described above, the resonance frequency has a problem that the deflection angle changes due to, for example, a change in the spring constant of the torsion beam depending on the temperature or a change in the viscous resistance of air due to atmospheric pressure.
For this reason, as disclosed in Patent Document 5, a deflection angle is detected by detecting a scanned beam, and control to keep the deflection angle stable is performed by adjusting an applied current applied to the vibrating mirror. ing.
Patent Document 6 discloses an example in which a light beam is detected by a synchronization detection sensor without using a scanning lens, and Patent Document 7 discloses an optical scanning apparatus using a diffractive optical element.

Japanese Patent No. 2924200 Japanese Patent No. 30111144 Japanese Patent No. 3445691 Japanese Patent No. 3543473 JP 2004-279947 A JP 2005-56245 A Japanese Patent No. 3559710

By using a vibration mirror instead of a polygon mirror, noise and power consumption can be reduced, and an image forming apparatus suitable for an office environment can be provided. Further, the housing can be reduced in weight and cost by reducing the thickness of the housing.
However, as described above, the oscillating mirror operates using the resonance phenomenon. Therefore, when the mirror width 2r is increased, the scanning speed does not increase and the deflection angle also decreases.
Further, since it is manufactured by a semiconductor process using a Si wafer, it is desirable that the mirror width 2r is as small as possible in order to make use of the features of the process even from the viewpoint of the characteristics and the number of microfabrication.
On the other hand, the beam spot diameter on the surface to be scanned and the light beam diameter of the light beam incident on the vibrating mirror are inversely proportional, and in order to obtain a very small beam spot diameter, the mirror width 2r must be increased. I must.
In addition, since the mirror itself is as thin as several hundred μm, the inertial force and air resistance acting against the amplitude operation increase as the mirror width 2r increases, and the mirror deforms to wave. This is a factor that degrades the beam spot diameter.

Therefore, the mirror width 2r is preferably as small as possible. However, if the effective scanning rate (θd / θ0) represented by the ratio of the angle of view θd for scanning the scanning area with respect to the amplitude θ0 is large, the main scanning direction on the surface to be scanned is large. Dot spacing between pixels along the line, so-called linearity, accelerates as the deflection angle increases, making it impossible to make corrections in the imaging optical system. In order to ensure the uniformity of the interval, the effective scanning rate (θd / θ0) must be kept at about 50%, the optical path length is extended, and in order to narrow the beam spot on the surface to be scanned, an appropriate mirror width 2r is required. It is necessary.
Furthermore, as higher image quality is desired, the beam spot is required to be reduced in diameter to faithfully reproduce high-definition dots, and this is becoming a disadvantageous condition for reducing the mirror width 2r. .

  An object of the present invention is to provide an optical scanning device capable of reducing the mirror width 2r as much as possible and capable of forming a high-quality image, and an image forming apparatus having the optical scanning device.

In order to achieve the above object, in the present invention, the direction of the vibrating mirror surface, the light beam incident on the vibrating mirror from the light source, the synchronization detection sensor with respect to the beam diameter d0 of the light beam required by reducing the beam spot diameter. The mirror width 2r can be minimized by setting the relationship with the arriving light beam to a predetermined condition.
Specifically, in the first aspect of the invention, the light source means, a vibrating mirror that is supported by a torsion beam, deflects the light beam from the light source means, and reciprocally scans the surface to be scanned, and the vibration mirror has a period. Oscillating mirror driving means for generating a rotational force automatically, an imaging optical system for imaging a light beam scanned by the oscillating mirror on the scanned surface,
And a light detecting means for detecting a light beam deflected by the vibrating mirror at a predetermined position in the main scanning direction, the light beam incident on the vibrating mirror and the optical axis of the imaging optical system. Is an angle (incident angle), 2θs is the angle between the light beam deflected to be incident on the light detection means and the optical axis of the imaging optical system, and the amplitude of the vibrating mirror is θ0. Then,
θ0 ≧ α / 2> θs
It is characterized by satisfying the following relationship.

According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the light detecting means detects the light beam deflected by the oscillating mirror without passing through the imaging optical system. Features.
According to a third aspect of the present invention, in the optical scanning device according to the second aspect, an image is formed on at least one surface of an optical element constituting the imaging optical system in the main scanning direction accompanying a wavelength change of the light source means. It has a diffractive surface whose power is set so as to correct the movement of the position.
According to a fourth aspect of the present invention, in the optical scanning device according to the first aspect, the light beam deflected to reach the scanning region end on the surface to be scanned and the optical axis of the imaging optical system. Assuming that the formed angle is 2θd, the amplitude center of the vibrating mirror is relative to the optical axis of the imaging optical system.
α / 2-θd
It is characterized by being arranged so as to tilt only.

According to a fifth aspect of the present invention, in the optical scanning device according to the fourth aspect, at least one surface of the optical element constituting the imaging optical system has a curved surface that is asymmetric in the main scanning direction with respect to the optical axis. It is characterized by that.
According to a sixth aspect of the present invention, in the optical scanning device according to the fourth aspect, at least one of a pulse period or a phase of a clock for modulating the light source means is varied according to a main scanning position. It is characterized by providing.
According to a seventh aspect of the present invention, in the optical scanning device according to the first aspect, the vibration mirror driving means calculates the amplitude of the vibration mirror based on the detection signal detected by the light detection means. The rotational force is controlled so that the deflection angle is constant.
In the invention according to claim 8, in the optical scanning device according to claim 1,
In the light source means, the deflection angle of the vibrating mirror is at least θ0 ≧ θ ≧ α / 2.
The light source driving means for prohibiting the light emission in the range is provided.

According to a ninth aspect of the present invention, the image forming apparatus includes the optical scanning device according to any one of the first to eighth aspects, wherein the oscillating mirror is driven at a predetermined scanning frequency, and forward scanning or recovery is performed. During any period of scanning, the light source means is modulated in accordance with image information to form an electrostatic latent image on an image carrier, the electrostatic latent image is visualized, and the visible image is recorded on a recording medium. The image is formed by transferring the image to the image.
According to a tenth aspect of the present invention, an image forming apparatus includes the optical scanning device according to any one of the first to eighth aspects, wherein a plurality of the vibrating mirrors are arranged and driven at a common scanning frequency, During either the forward scan or the backward scan, the light source means is modulated according to the image information to form an electrostatic latent image on the image carrier corresponding to each color, and the electrostatic latent image is visualized. And the visible image is superimposed on a transfer member and transferred onto a recording medium to form a multicolor image.
According to an eleventh aspect of the present invention, in the image forming apparatus according to the tenth aspect, image recording of each color is performed by aligning the scanning directions of the plurality of vibrating mirrors.

According to the first aspect of the present invention, even if the effective scanning rate (θd / θ0) is kept low in order to ensure the uniformity of the dot spacing along the main scanning direction on the surface to be scanned, the amplitude θ0 The incident angle α of the light beam from the light source means to the vibrating mirror can be kept to a minimum.
In addition, by arranging the light beam reaching the light detection means for obtaining the synchronization detection signal on the start side of the scanning area on the scanned surface, the deflection angle of the vibrating mirror that scans the end side of the scanning area is minimized, The maximum deflection angle 2θmax in the vibrating mirror can be minimized, and the mirror width can be minimized.
Accordingly, it is possible to cope with the reduction in the beam spot diameter and the uniformity of the dot interval in the main scanning direction, and high-quality image formation can be performed.

According to the second aspect of the present invention, the angle formed by the light beam reaching the light detection means and the light beam reaching the start end of the scanning region is not reduced by passing through the imaging optical system having a positive power. As a result, the light beam can be separated even if the deflection angle difference θs−θd at the oscillating mirror is smaller, so that the incident angle α of the light beam from the light source means to the oscillating mirror can be kept small, and the mirror width can be minimized. Limit.
In addition, each optical element constituting the imaging optical system is not affected by the movement of the imaging position in the main scanning direction that occurs in accordance with the change in the wavelength of the light source means. Since the deflection angle θs can be directly detected, the above-described deflection angle can be more reliably controlled, and high-quality image formation can be performed.

According to the third aspect of the present invention, even if the light beam deflected by the oscillating mirror is detected and the synchronization detection signal is obtained without using the imaging optical system, the scanning lens constituting the imaging optical system can be obtained. Since the deviation of the image writing start position can be reduced without being affected by the change in the refractive index due to temperature and the change in the curvature of the lens surface, a high-quality image can be formed.
According to the fourth aspect of the present invention, the normal direction of the vibrating mirror is determined with respect to the minimum required maximum deflection angle 2θmax of the vibrating mirror, thereby eliminating the waste of amplitude and minimizing it. In addition, since the mirror width can be minimized, it is possible to cope with the reduction of the beam spot diameter and the uniformity of the dot interval along the main scanning direction, and high-quality image formation can be performed.

According to the fifth aspect of the present invention, even if the normal direction of the oscillating mirror, in other words, the amplitude center is arbitrarily set with respect to the optical axis of the imaging optical system, the scanned object is based on the amplitude center. The dot interval along the main scanning direction can be made uniform on the surface, and high-quality image formation can be performed.
According to the sixth aspect of the present invention, even if the normal direction of the oscillating mirror, in other words, the amplitude center is arbitrarily set with respect to the optical axis of the imaging optical system, the scanned object is based on the amplitude center. The dot interval along the main scanning direction can be made uniform on the surface, and high-quality image formation can be performed.
According to the seventh aspect of the present invention, even if there is a change in the spring constant of the torsion beam or a change in the air resistance caused by changes in the operating environment, that is, the temperature or the atmospheric pressure, the deflection angle changes. Therefore, it is possible to ensure that the uniformity of the dot interval along the main scanning direction is stably maintained, and high-quality image formation can be performed.

According to the invention described in claim 8, by setting the output of the light source only in the range of α / 2>θ> θs, it is possible to reliably prevent the light beam deflected by the vibrating mirror from returning to the light source. Therefore, an output setting error can be eliminated and the beam intensity can be stably maintained on the surface to be scanned, so that high-quality image formation can be performed.
According to the ninth aspect of the present invention, an image forming apparatus with low noise and low power consumption can be realized by using a vibrating mirror.
According to the tenth aspect of the present invention, by using the vibration mirror, it is possible to realize an image forming apparatus with low noise and low power consumption and compatible with a tandem color engine.
According to the eleventh aspect of the invention, by performing the image recording of each color with the scanning directions of the plurality of vibrating mirrors aligned, the writing direction is aligned, and high-quality image formation can be performed.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 shows an example of an optical scanning apparatus 900A that scans four stations (color-forming image forming stations), and divides each of the two stations into two, and each beam is applied to a pair of vibrating mirrors 460 arranged in opposite directions. The method of deflecting and scanning is shown.
The four photosensitive drums 101, 102, 103, 104 are arranged at equal intervals along the moving direction (arrow direction) of the intermediate transfer belt 105 as a transfer member, and sequentially transfer toner images of different colors to the intermediate transfer belt 105. A color image is formed by superimposing them.
The optical scanning device 900A that scans each photosensitive drum is integrally formed, and scans beams from light source units corresponding to each of the photosensitive drums, which will be described later, by vibrating mirrors 460 provided individually.

The oscillating mirror 460 is arranged back-to-back in parallel with the center of the optical scanning device 900A, and deflects and scans the light beams from the light source units incident at a predetermined angle in the sub-scanning direction.
The light source units 107, 108, 109, 110 as the light source means or the light source device are arranged so that the emission positions of the light source units 107, 110 are shifted from the light source units 108, 109 by a predetermined interval, and from the light source units 107, 108. The light beams 201 and 202 and the light beams 203 and 204 from the light source units 109 and 110 are symmetric so that the light beams corresponding to the scanning angle θ = 0, which are deflected when the vibrating mirrors 460 are stationary, are aligned coaxially. An image is simultaneously written on the photosensitive drum corresponding to each of yellow, cyan, magenta, and black.
At this time, if one of the oscillating mirrors delays the ½ cycle timing based on a detection signal from a synchronization detection sensor described later and writes an image at the time of backward scanning of the oscillating mirror, The scanning direction can be aligned.

The beams 201, 202, 203, and 204 from each light source unit are arranged so that the incident angle in the main scanning direction is 35 ° (= α / 2 + θd) with respect to the normal line of each oscillating mirror. , 109 are folded back by the incident mirrors 111 and 112, and the respective optical mirrors 460 are aligned with the main scanning direction with the optical paths of the light beams 201 and 204 from the light source units 107 and 110 directly toward the vibrating mirror. Are respectively incident horizontally.
One of the cylinder lenses 113, 114, 115, and 116 has a flat curvature, the other has a common curvature in the sub-scanning direction, and is disposed so that the optical path lengths to the deflection point of the vibrating mirror 460 are equal. The light beams from the light source units 107, 108, 109, and 110 are made to enter the sub-scanning direction while being vertically shifted with the optical axis in between, so that the light beams are bent by the refractive power and intersect in the vicinity of the deflection surface. Is obliquely incident on.

Each light beam is converged so as to be linear in the main scanning direction on the deflection surface, and in combination with a toroidal lens described later, the surface tilt correction optical system in which the deflection point and the photosensitive drum surface are conjugated in the sub-scanning direction. Make.
After the deflection, the beams are incident on the scanning lenses (hereinafter also referred to as “fθ lenses”) 120 and 121 while widening the interval so that the beams are separated from each other. The scanning lenses 120 and 121 are formed by resin molding, so that the f · arcsin characteristic corresponding to the sine wave vibration of the vibrating mirror in the main scanning direction, that is, the change dH / dθ of the main scanning position per unit scanning angle is sin−1 ( It has a non-arc surface shape with power (refractive power) so as to have a characteristic proportional to θ / θ0), and the beam moves at a substantially constant speed on the surface of the photosensitive drum as the vibrating mirror rotates. The main scanning position corresponding to each pixel is corrected, and each beam is formed in a spot shape on the surface of the photoreceptor by the subsequent toroidal lenses 122, 123, 124, and 125, and a latent image is recorded.

As shown in FIG. 2, the toroidal lens has a Fresnel diffraction surface formed of a sawtooth diffraction grating on the first surface, and when the wavelength of the light source is increased, the imaging position in the main scanning direction becomes the optical axis. The power by diffraction is given so that it may approach.
In general, since the power of the imaging optical system is positive, the refractive power becomes weaker as the wavelength increases, and the imaging position moves away from the optical axis in the main scanning direction. By setting the diffraction power so as to be in the opposite direction, consideration is given to avoiding a difference in magnification between stations.
In this embodiment, the oscillating mirror of each color station is arranged so that the rotation axis coincides with the center of the image in the main scanning direction, and the optical path lengths from the oscillating mirror to the surface of the photosensitive drum coincide with each other and are arranged at equal intervals. Three folding mirrors are arranged per station so that the incident positions and incident angles with respect to the respective photosensitive drums are equal.

Referring to FIG. 1, the optical path for each color station will be described. The beam 201 from the light source unit 107 is tilted downward through the cylinder lens 113, enters the vibrating mirror 460, and passes through the scanning lens 120. Then, it is reflected by the folding mirror 126, passes through the toroidal lens 122, is reflected by the folding mirrors 127, 128, and is guided to the photosensitive drum 102 to form a magenta image as the second station.
The beam 202 from the light source unit 108 is tilted upward via the cylinder lens 114, reflected by the incident mirror 111, incident on the oscillating mirror 460, passes through the scanning lens 120, is reflected by the folding mirror 129, and is toroidal. The light passes through the lens 123, is reflected by the folding mirrors 130 and 131, is guided to the photosensitive drum 101, and forms a yellow image as the first station.
The same applies to the third and fourth stations arranged symmetrically, and the beam 203 from the light source unit 109 is deflected by the oscillating mirror 460 via the incident mirror 112, reflected by the folding mirror 132, and passes through the toroidal lens 125. Then, the light is reflected by the folding mirrors 133 and 134 and guided to the photosensitive drum 104, and the black image is used as the fourth station, and the beam 204 from the light source unit 110 is deflected by the vibrating mirror 460 and is reflected by the folding mirror 135. The reflected light passes through the toroidal lens 124, is reflected by the folding mirrors 136 and 137, is guided to the photosensitive drum 103, and forms a cyan image as a third station.
These components are integrally held in a single housing described later.

One set of substrates on which synchronization detection sensors 138 and 140 as light detection means are mounted are provided for two opposing stations, and a beam is detected outside the photoconductor scanning area on the light source side. Next, the timing for writing the image by generating the synchronization detection signal for each station is taken.
As shown in FIG. 3, when the diameter of the incident light beam is d0, the vibrating mirror 460 uses the maximum deflection angle 2θmax as the width 2r in the direction orthogonal to the rotation axis.
2r ≧ d0 / cos θmax
It is necessary to.
However, as described above, increasing r increases the moment of inertia I, which is disadvantageous with respect to the resonance frequency and deflection angle. Therefore, θmax is preferably as small as possible.

Conventionally, the relationship between the incident angle α from the light source unit to the vibrating mirror surface and the deflection angle (amplitude) of the vibrating mirror is θ0.
α> 2θ0
And the maximum deflection angle 2θmax = α + 2θ0
I was trying
In the present embodiment, the light beams deflected by the vibrating mirror 460 pass through the scanning lenses 120 and 121 and are focused and incident by the imaging lenses 139 and 141 to the synchronization detection sensors 138 and 140. Then, as shown in FIG.
2θ0 ≧ α>2θs> 2θd
Here, θd is an effective deflection angle for scanning on the photosensitive member, and θs is a relationship of a deflection angle at the time of synchronization detection.
Specifically, θ0 = 25 °, θd = 15 °, α = 40 °, and θs = 18 °.

Conventionally, the incident angle α to the vibrating mirror surface is inclined by α / 2 with respect to the normal line of the vibrating mirror surface at rest, and the center of amplitude coincides with the optical axis of the scanning lens. However, in the present embodiment, the amplitude center is Δθ = α / 2-2θd from the optical axis.
A pulse of a clock that modulates the semiconductor laser as described later, or at least one surface of the scanning lens or toroidal lens has an asymmetric curved surface shape along the main scanning direction so as to be inclined only toward the light source side. By varying the period or phase according to the main scanning position, the deviation of the imaging position in the main scanning direction that occurs when the amplitude center of the oscillating mirror and the optical axis of the scanning lens do not match is corrected. I am doing so.
In this way, the maximum deflection angle can be reduced to 2θmax = α + 2θd, and the mirror width 2r can be minimized.

As shown in FIG. 1, the exit roller portion (left end portion in FIG. 1) of the intermediate transfer belt 105 is provided with detection means for detecting the overlay accuracy of each color image formed and superimposed at each station. ing.
The detection means reads the detection pattern of the toner image formed on the intermediate transfer belt 105 to detect the main scanning resist and the sub-scanning resist as deviations from the reference station, and periodically performs correction control.
In this embodiment, the detection means includes an LED element 154 for illumination, a photosensor 155 that receives reflected light, and a pair of condensing lenses 156. The detection means is provided at three positions, the left and right ends and the center of the image, and intermediate transfer. As the belt 105 moves, the difference in detection time from the reference color black is read.

FIG. 5 is an exploded perspective view of the vibrating mirror module used in the optical scanning device according to the present embodiment.
Here, an example of an electromagnetic drive method will be described as a method for generating the rotational torque of the vibrating mirror. As shown in the figure, the movable mirror 441 that forms the mirror surface of the oscillating mirror is pivotally supported by a torsion beam 442 and, as will be described later, is manufactured by penetrating the outer shape by etching from a single Si substrate. The vibrating mirror substrate 440 is configured as a unit that is mounted on the 448 and integrally includes the vibrating mirror. In FIG. 1 and FIG. 8, the mounting substrate 448 is omitted.
In this embodiment, a module in which a pair of vibration mirror substrates 440 are integrally supported back to back is formed.
The support member 445 is formed of resin and is positioned at a predetermined position of the circuit board 449. The vibration mirror substrate 440 is arranged such that the torsion beam 442 is orthogonal to the main scanning plane and each mirror surface has a predetermined angle with respect to the main scanning direction. Here, the positioning part 451 for positioning the mirror surfaces parallel to each other so as to be inclined by 30 °, and the wiring terminal 455 formed on one side of the mounting substrate 448 of the vibration mirror substrate 440 are made of metal so that they contact each other at the time of mounting. The edge connector portion 452 in which the terminal group is arranged is integrally configured.
In this embodiment, the support member 445 and the circuit board 449 are separate members, but either one may serve as the other.

The vibrating mirror substrate 440 has one side inserted into the edge connector 452 and is fitted inside the presser claw 453. The both sides of the back of the substrate are supported along the positioning portion 451, and electrical wiring is provided. At the same time, each vibrating mirror substrate 440 can be individually replaced.
The circuit board 449 is mounted with a control IC, a crystal oscillator, and the like that constitute a drive circuit for the vibrating mirror, and a power supply and a control signal are input / output via the connector 454.
Further, by shifting the amplitude phase of each oscillating mirror by ½ period, the scanning direction can be made uniform even when deflected in the opposite directions.

As shown in FIG. 6, the oscillating mirror module 470 is mounted on a housing (optical housing) 400 that integrally forms a side wall 457 erected so as to surround the oscillating mirror module 470, and an upper end edge of the side wall 457. Is sealed by an upper cover 458.
A flat transmission window 459 is provided at the opening of the side wall 457 for entering and exiting the light beam. The transmission window 459 is disposed so as to be inclined by about 5 ° in the sub-scanning direction with respect to the vibrating mirror surface (movable mirror 441), and consideration is given so that the light beam is not repeatedly reflected between the vibrating mirror surface.
The upper cover 458 is bonded with foamed polyurethane or the like to ensure heat insulation so as to suppress heat propagation from the outside air.

Next, details of the vibrating mirror substrate 440 will be described with reference to FIGS. 7 and 8 (disassembled perspective views).
The oscillating mirror 460 includes a movable part that forms a mirror surface on the surface and forms a vibrator, a torsion beam that supports the movable part, and a frame that forms a support part, and is formed by cutting an Si substrate by etching.
In this embodiment, as shown in FIG. 7C, the wafer is manufactured using a wafer in which two substrates of 60 μm and 140 μm called SOI substrates are bonded in advance with an oxide film interposed therebetween.
First, a torsion beam 442, a vibration plate 443 on which a planar coil is formed, a reinforcing beam 444 that forms a skeleton of a movable part, a frame 446, and the like by a dry process by plasma etching from the surface side of a 140 μm substrate (second substrate) 461 The remaining part of the film is penetrated to the oxide film.
Next, from the surface side of the 60 μm substrate (first substrate) 462, the other portions except the movable mirror 441 and the frame 447 are penetrated to the oxide film by anisotropic etching such as KOH, and finally, The oxide film around the movable part is removed and separated to form a vibrating mirror structure.

Here, the torsion beam 442 and the reinforcing beam 444 had a width of 40 to 60 μm. As described above, it is desirable that the moment of inertia I of the vibrator is small in order to increase the deflection angle. On the other hand, the mirror surface is deformed by the inertial force. .
Further, an aluminum thin film is deposited on the surface side of the 60 μm substrate 462 to form a reflective surface. As shown in FIG. 7B, the surface of the 140 μm substrate 461 is twisted with a coil pattern 463 as a planar coil made of a copper thin film. A terminal 464 wired through the beam 442 and a patch 465 for trimming are formed.
Naturally, a configuration may be adopted in which a thin film permanent magnet is provided on the diaphragm 443 side and a planar coil is formed on the frame 447 side.

On the mounting substrate 448, a frame-shaped base 466 on which the vibration mirror 460 is mounted and a yoke 449 formed so as to surround the vibration mirror 460 are provided. The yoke 449 faces the end of the movable mirror 441 and is respectively S. A pair of permanent magnets 450 that join a pole and an N pole and generate a magnetic field in a direction orthogonal to the rotation axis are joined.
The vibrating mirror 460 is mounted on the pedestal 466 with the mirror surface facing up, and a current flows between the terminals 464, whereby a Lorentz force is generated on each side parallel to the rotation axis of the coil pattern 463, and the torsion beam 442 is A rotational torque T that twists to rotate the movable mirror 441 is generated, and when the current is turned off, the moving mirror 441 returns horizontally due to the return force of the torsion beam 442.
Therefore, the movable mirror 441 can be reciprocally oscillated by alternately switching the direction of the current flowing through the coil pattern 463.

When the current switching period is made close to the natural frequency of the primary vibration mode with the torsion beam 442 as the rotation axis of the structure constituting the oscillating mirror 460, the so-called resonance frequency f0, the amplitude is excited and a large fluctuation occurs. You can get a corner.
Therefore, the scanning frequency fd is normally set or controlled so as to follow or follow the resonance frequency f0. However, as described above, the resonance frequency f0 is the moment of inertia of the vibrator constituting the vibration mirror 460. Therefore, when there are variations in the dimensional accuracy of the finished product, a difference occurs between individuals. When a plurality of vibrating mirrors are used as in this embodiment, it is difficult to align the scanning frequencies fd. Become.
The variation of the resonance frequency f0 is about ± 200 Hz depending on the capability of the process. For example, if the scanning frequency fd = 2 kHz, a deviation of the scanning line pitch corresponding to 1/10 line occurs. When line recording is performed, the scanning position is shifted by one line.
Those having close resonance frequencies f0 can be combined by sorting, but the production efficiency is poor, and it is necessary to always handle them in pairs when they are exchanged.

Therefore, in this embodiment, before mounting on the mounting substrate 448, the inertia moment I is obtained by gradually reducing the mass of the movable part by cutting the patch 465 formed on the back side of the movable part with a carbon dioxide gas laser or the like. In this case, adjustment is made so that the resonance frequency f0 is within ± 50 Hz so that the resonance frequency f0 substantially matches even if there is a dimensional difference between individuals.
The scanning frequency fd is set within the frequency band regardless of the resonance frequency f0.

FIG. 9 shows how the resonance frequency is adjusted by changing the mass (trimming).
A vibration corresponding to the scanning frequency is applied to the vibration mirror 460 by the vibration device, and a carbon dioxide laser is applied to the patch 465 from the back side of the vibration mirror 460, and a cut is made until the deflection angle sharply increases due to resonance. .
The resonance state can be detected by applying a beam from the front side of the oscillating mirror 460 with the light source device and detecting the shake of the reflected beam with the amplitude detection device.
It should be noted that, instead of such a reduction type trimming, an increase type method of attaching a balance weight may be used.

FIG. 10 is a block diagram of a drive circuit that amplifies the vibration mirror.
As described above, an AC voltage or a pulse wave voltage is applied to the planar coil (coil pattern 463) formed on the back side of the oscillating mirror so that the direction of current flow is switched alternately, and the deflection angle θ is constant. In such a manner, the reciprocal vibration is performed by adjusting the gain of the current flowing through the planar coil.
FIG. 11 shows the relationship between the frequency f for switching the current flow direction and the deflection angle θ. Generally, the frequency characteristic has a peak at the resonance frequency f0, and if the scanning frequency fd matches the resonance frequency f0, Large deflection angle. However, the swing angle changes steeply near the resonance frequency.
Therefore, initially, the drive frequency (vibration mirror drive means) of the movable mirror 441 can be set so that the drive frequency applied to the fixed electrode matches the resonance frequency. When the resonance frequency fluctuates, the deflection angle drastically decreases, and there is a disadvantage that the stability over time is poor.

Therefore, in this embodiment, the scanning frequency fd is fixed to a single frequency that is excluded from the resonance frequency f0, and the deflection angle θ can be increased or decreased according to gain adjustment.
Specifically, with respect to the resonance frequency f0 = 2 kHz, the scanning frequency fd is set to 2.5 kHz, and the deflection angle θ is adjusted to ± 25 ° by gain adjustment.
Over time, with respect to the deflection angle θ, a detection signal detected at the time of backward scanning and a detection signal detected at the time of forward scanning by the synchronous detection sensors 139 and 140 arranged at the start end of the scanning region of the beam scanned by the vibrating mirror 460 And the control is performed so that the deflection angle θ is constant.

As shown in FIG. 12, the oscillating mirror is resonantly oscillated, so that the scanning angle θ changes in a sin wave shape with time t. Therefore, when the maximum deflection angle of the vibrating mirror, that is, the amplitude is θ0,
θ = θ0 · sin2πfd · t
If the synchronous detection sensors 139 and 140 detect a beam whose scanning angle corresponds to 2θs, detection signals are generated in the backward scanning and the forward scanning, and using the time difference T,
θs = θ0 · cos2πfd · T / 2
Since θs is fixed, it can be seen that the maximum deflection angle θ0 can be detected by measuring T.
The period from the beam detection in the backward scan to the beam detection in the forward scan is the deflection angle of the vibrating mirror.
θ0>θ> θs
During a certain period, the light emission of the light source is prohibited. The light emission prohibition control is performed by a light source driving unit as a light source driving unit shown in FIG.
On the photosensitive drum surface that is the surface to be scanned, it is necessary to form main scanning dots so that the intervals between the pixels are uniform with respect to time.

As shown in FIG. 13, the rate of change of the deflection angle θ decreases with time in the vibrating mirror, so that the pixel interval extends on the surface to be scanned as it goes to both ends of the main scanning region.
In general, this deviation is corrected by using an f · arcsin lens as a scanning lens. However, as in the case of scanning with a polygon mirror, when the pixel clock is modulated at a single frequency, the scanning angle 2θ is time-dependent. In order to change in proportion, that is, at a constant speed, it is necessary to set the power (refractive power) along the main scanning direction so that the correction amount of the main scanning position is maximized at the end of the main scanning region.
At this time, assuming that the image height is 0, that is, the time from the image center to an arbitrary image height H is t, the relationship between the image height H and the shake angle θ (scanning angle 2θ) is
H = ω · t = (ω / 2πfd) · sin−1 (θ / θ0)
It becomes. Here, ω is a constant.

However, as the amount of correction of the so-called linearity of the pixel spacing increases, the power deviation along the main scanning direction of the scanning lens increases, and the change in the beam spot diameter corresponding to each pixel on the scanned surface also increases. End up.
In addition, since the center of amplitude of the vibrating mirror and the optical axis do not coincide with each other as described above, a scanning lens having an asymmetric curved surface on the optical axis is required. In this embodiment, the phase Δt of the pixel clock is set to the main scanning. By varying according to the position, the deviation of the power of the scanning lens along the main scanning direction is made as small as possible, and the asymmetric component is corrected.

Now, assuming that the change in the scanning angle accompanying the change in the phase Δt of the pixel clock is 2Δθ,
H = (ω / 2πfd) · sin−1 {(θ−Δθ) / θ0}
Δθ / θ0 = sin2πfdt−sin2πfd (t−Δt)
The following relational expression is obtained.
Here, when the scanning lens has power distribution close to that of the fθ lens and the residual is corrected by the phase Δt of the pixel clock,
H = (ω / 2πfd) · {(θ−Δθ) / θ0}
= (Ω / 2πfd) · sin−1 (θ / θ0)
Δθ / θ0 = θ / θ0-sin-1 (θ / θ0)
The phase Δt (sec) of the predetermined pixel along the main scanning direction is
(Θ / θ0) −sin−1 (θ / θ0) = sin2πfdt−sin2πfd (t−Δt)
What is necessary is just to modulate a light emission source so that it may be determined based on the following relational expression.

FIG. 14 is a block diagram of a driving circuit for modulating a semiconductor laser that is a light emitting source.
The image data rasterized for each color is temporarily stored in the frame memory, read out sequentially to the image processing unit, and the pixel data of each line according to the matrix pattern corresponding to the halftone while referring to the relationship between before and after. Are transferred to the line buffer corresponding to each light source.
The write control unit reads each from the line buffer using the synchronization detection signal as a trigger, and modulates it independently.

Next, a clock generation unit (pixel clock generation unit) that modulates each light emitting point will be described. The counter counts the high-frequency clock VCLK generated by the high-frequency clock generation unit, and the comparison circuit gives this count value, a preset value L set in advance based on the duty ratio, and the pixel clock transition timing from the outside. The phase data H indicating the phase shift amount is compared, and when the count value coincides with the set value L, the control signal l instructing the falling edge of the pixel clock PCLK is compared with the phase data H. A control signal h instructing rising of the clock PCLK is output. At this time, the counter is reset simultaneously with the control signal h and counting from 0 is performed again, whereby a continuous pulse train can be formed.
In this way, the phase data H is given for each clock, and the pixel clock PCLK whose pulse cycle is sequentially changed is generated. Here, the pixel clock PCLK is divided by 8 of the high-frequency clock VCLK so that the phase can be varied with a resolution of 1/8 clock. This variable control is performed by a light source driving unit as a light source driving unit shown in FIG.

FIG. 15 is an example in which the phase of an arbitrary pixel is shifted, and is an example in which the phase is delayed by 1/8 clock.
When the duty is 50%, a set value L = 3 is given, and the counter counts 4 and the pixel clock PCLK falls. Assuming that the 1/8 clock phase is delayed, phase data H = 6 is given and rises with 7 counts. At the same time, the counter is reset, so it falls again at 4 counts. That is, the adjacent pulse period is shortened by 1/8 clock.
The pixel clock PCLK generated in this way is supplied to the light source driving unit, and the semiconductor laser is driven by the modulation data in which the pixel data read from the line buffer is superimposed on the pixel clock PCLK.

FIG. 16 shows the correction amount of the main scanning position in each pixel according to the main scanning position when modulated at a single frequency. The main scanning area is divided into a plurality of areas, and in the embodiment, the main scanning area is divided into eight areas. Then, by approximating with a polygonal line, the number of phase shifts is set for each region so that the main scanning position deviation is zero at the boundary of each region, and correction is made in a staircase pattern.
For example, assuming that the number of pixels in the i region is Ni, the shift amount in each pixel is 1/16 unit of the pixel pitch p, and the deviation of the main scanning position at both ends of each region is ΔLi,
ni = Ni · p / 16ΔLi
Therefore, the phase may be shifted for each ni pixel.
Assuming that the pixel clock is fc, the total phase difference Δt uses the number of phase shifts Ni / ni, and Δt = 1 / 16fc × ∫ (Ni / ni) di.
Similarly, the phase difference Δt in the pixel of the Nth dot can also be set by the cumulative number of phase shifts so far.

Note that the divided region width may be equal or unequal, and the number of divisions may be any number. However, when the shift amount in each pixel is increased, the step is easily noticeable on the image. Therefore, it is desirable that the pixel pitch p is equal to or less than ¼ unit. Conversely, if the phase shift amount is small, the number of phase shifts increases and the memory capacity increases. Also, the smaller the number of divisions, the smaller the memory capacity. Therefore, it is efficient to set the area width of the area where the main scanning position deviation is large and to increase the area width of the small area.
The output of the semiconductor laser is generally detected before the back light is applied to the image area for each scan by a light amount monitor sensor mounted in the same package, and is emitted so as to maintain a constant value during one line recording. Control the amount of current applied to the source.

FIG. 17 shows an example of an image forming apparatus equipped with the optical scanning device 900A shown in FIG.
Around the black photosensitive drum 104, a charging charger 902 that charges the photosensitive drum to a high voltage, and a developing device 904 that attaches and charges the electrostatic latent image recorded by the optical scanning device 900A. A cleaning device 905 that scrapes and stores toner remaining on the photosensitive drum is disposed. The peripheral configuration of the other photosensitive drums is the same. Image recording is performed on the photosensitive drum every two lines in one cycle by reciprocating scanning of the vibrating mirror.
The above-described image forming stations are arranged in parallel in the moving direction of the intermediate transfer belt 105, and toner images of yellow, magenta, cyan, and black are sequentially transferred onto the intermediate transfer belt 105 at the appropriate timing, and are superimposed to form a color image. The
Each image forming station has basically the same configuration except that the toner color is different.

  On the other hand, a recording sheet as a recording medium is supplied from a sheet feeding tray 907 by a sheet feeding roller 908 and is sent out by a registration roller pair 909 in accordance with the recording start timing in the sub-scanning direction, and a toner image is transferred from the intermediate transfer belt 105. Is done. Thereafter, fixing is performed by the fixing device 910, and the sheet is discharged onto the discharge tray 911 by the discharge roller pair 912.

A second embodiment will be described with reference to FIG. In addition, the same part as the said embodiment is shown with the same code | symbol, and unless it was especially required, the description on the structure and function which were already demonstrated is abbreviate | omitted, and only the principal part is demonstrated.
In the present embodiment, a system is shown in which four stations are scanned by a single vibrating mirror.
As shown in the figure, the optical scanning device 900B that scans each of the photosensitive drums 101, 102, 103, and 104 is integrally configured, and is arranged at equal intervals along the moving direction (arrow direction) of the intermediate transfer belt 105. For the two photosensitive drums 101, 102, 103, and 104, the beams from the light source units 107, 108, 109, and 110 corresponding to the respective photosensitive drums 101, 102, 103, and 104 are separated again after being deflected by the oscillating mirror 460, and guided simultaneously. Form.
The beams from the respective light source units are obliquely incident on the vibration mirror 460 at different incident angles in the sub-scanning direction, so that the beams from the respective light source units are collectively deflected and scanned.

The light source units 107, 108, 109, and 110 are radially arranged so that the light source unit 110 is the highest and the lowest in order so that the height differs in the sub-scanning direction.
Beams 203, 202, and 201 from other light source units are vertically aligned in the order of beams 203, 202, and 201 by three incident mirrors 111 having different heights in a stepped manner. They are folded back so as to be aligned, are incident on the cylinder lens 113 with different heights in the sub-scanning direction, and head toward the vibrating mirror 460.

Each beam crosses in the sub-scanning direction near the oscillating mirror surface by the cylinder lens 113 and is incident on the fθ lens 120 after being deflected while widening the distance so that the beams are separated from each other.
The fθ lens 120 is shared by all stations and has no convergence in the sub-scanning direction. Of the beams from the respective light source units that have passed through the fθ lens 120, the beam from the light source unit 107 is reflected by the folding mirror 126, forms an image on the photosensitive drum 101 via the toroidal lens 122, and forms a first image. A latent image based on yellow image information is formed as one image forming station.
The beam from the light source unit 108 is reflected by the folding mirror 127, forms a spot image on the photosensitive drum 102 via the toroidal lens 123 and the folding mirror 128, and forms magenta image information as a second image forming station. A latent image based on the image is formed.

The beam from the light source unit 109 is reflected by the folding mirror 129, forms a spot image on the photosensitive drum 103 via the toroidal lens 124 and the folding mirror 130, and cyan image information as a third image forming station. A latent image based on the image is formed.
The beam from the light source unit 110 is reflected by the folding mirror 131, forms a spot image on the photosensitive drum 104 via the toroidal lens 125 and the folding mirror 132, and serves as a fourth image forming station for black image information. A latent image based on the image is formed.
Similarly, the light beam deflected by the oscillating mirror 460 passes through the side of the scanning lens 120 and is focused and incident by the imaging lens 139 to the synchronization detection sensor 138, and based on the detection signal. A synchronization detection signal is generated for each station.
The optical scanning device 900B in the present embodiment can also be provided in the image forming apparatus in the same manner as the optical scanning device 900A in the first embodiment.

1 is a perspective view of an optical scanning device according to a first embodiment of the present invention. It is a figure which shows the shape of the toroidal lens in an imaging optical system, (a) is a side view, (b) is a plane sectional view. It is a figure which shows the relationship between the width | variety of the direction orthogonal to the rotating shaft in a vibration mirror, and the diameter of the incident light beam. It is a figure which shows the relationship between the incident angle of the beam to a vibration mirror surface, the deflection angle of a vibration mirror, the effective deflection angle which scans a photoreceptor, and the deflection angle at the time of a synchronous detection. It is a disassembled perspective view of a vibration mirror module. It is a disassembled perspective view which shows the mounting state of the vibration mirror module to a housing. It is a figure which shows a vibration mirror board | substrate, (a) is a whole front view, (b) is a rear view of a mirror part, (c) is a schematic sectional drawing which shows the joining state of the board | substrate of a vibration mirror. It is a disassembled perspective view of a vibration mirror substrate. It is a figure which shows the adjustment method of the resonant frequency by variable of the mass of a vibration mirror. It is a block diagram of the drive circuit which makes a vibration mirror amplitude. It is a figure which shows the relationship between the frequency which switches the direction through which an electric current flows, and a deflection angle. It is a figure which shows the change of the scanning angle accompanying the resonant vibration of a vibration mirror. It is a figure which shows the change rate of the deflection angle with time progress of a vibration mirror. It is a block diagram of the drive circuit for modulating the light emission source (semiconductor laser) of a light source means. It is explanatory drawing at the time of shifting the phase of arbitrary images. It is a figure which shows the correction amount of the main scanning position in each pixel according to the main scanning position at the time of modulating with a single frequency. 1 is a schematic configuration diagram of an image forming apparatus. It is a perspective view of the optical scanning device in a 2nd embodiment. It is a conceptual diagram of the width | variety of the direction orthogonal to the rotating shaft in a vibration mirror.

Explanation of symbols

101, 102, 103, 104 Photosensitive drum as scanning surface or image carrier 107.108, 109, 110 Light source unit 120, 121 as light source means Scan lens 122, 123, as optical element of imaging optical system 124, 125 Toroidal lenses as optical elements of the imaging optical system 138, 140 Synchronous detection sensor as light detection means 460 Vibration mirror

Claims (11)

Light source means;
A vibrating mirror supported by a torsion beam and deflecting a light beam from the light source means to reciprocately scan a surface to be scanned;
Oscillating mirror driving means for periodically generating a rotational force in the oscillating mirror;
An imaging optical system that forms an image of the light beam scanned by the vibrating mirror on the surface to be scanned;
Light detecting means for detecting the light beam deflected by the vibrating mirror at a predetermined position in the main scanning direction;
In an optical scanning device having
The angle between the light beam incident on the vibrating mirror and the optical axis of the imaging optical system is α (incident angle), and the light beam deflected to enter the light detection means and the imaging optics When the angle between the optical axis of the system is 2θs and the amplitude of the vibrating mirror is θ0,
θ0 ≧ α / 2> θs
An optical scanning device characterized by satisfying the following relationship: The optical scanning device according to claim 1,
The optical scanning device characterized in that the light detection means detects the light beam deflected by the vibrating mirror without going through the imaging optical system. The optical scanning device according to claim 2,
A diffractive surface whose power is set so as to correct the movement of the imaging position in the main scanning direction accompanying the wavelength change of the light source means is provided on at least one surface of the optical element constituting the imaging optical system. Optical scanning device. The optical scanning device according to claim 1,
Assuming that the angle between the light beam deflected to reach the scanning region end on the surface to be scanned and the optical axis of the imaging optical system is 2θd, the amplitude center of the vibrating mirror is the center of the imaging optical system. For the optical axis
α / 2-θd
An optical scanning device characterized by being arranged so as to be inclined only. The optical scanning device according to claim 4.
An optical scanning device characterized in that at least one surface of an optical element constituting the imaging optical system has a curved surface that is asymmetric in the main scanning direction with respect to the optical axis. The optical scanning device according to claim 4.
An optical scanning apparatus comprising light source driving means for varying at least one of a pulse period or a phase of a clock for modulating the light source means in accordance with a main scanning position. The optical scanning device according to claim 1,
The oscillating mirror driving means calculates the amplitude of the oscillating mirror based on the detection signal detected by the light detecting means, and controls the rotational force so that the deflection angle becomes constant. Scanning device. The optical scanning device according to claim 1,
In the light source means, the deflection angle of the vibrating mirror is at least θ0 ≧ θ ≧ α / 2.
An optical scanning device comprising light source driving means for prohibiting light emission in the range of. An optical scanning device according to any one of claims 1 to 8,
The vibrating mirror is driven at a predetermined scanning frequency, and an electrostatic latent image is formed on the image carrier by modulating the light source means according to image information during either forward scanning or backward scanning. An image forming apparatus characterized in that the electrostatic latent image is visualized and the visible image is transferred to a recording medium to form an image. An optical scanning device according to any one of claims 1 to 8,
A plurality of the vibrating mirrors are arranged and driven at a common scanning frequency, and the light source means is modulated according to image information on an image carrier corresponding to each color during either forward scanning or backward scanning. An image forming apparatus that forms an electrostatic latent image, visualizes the electrostatic latent image, superimposes the visible image on a transfer body, transfers the image to a recording medium, and forms a multicolor image. . The image forming apparatus according to claim 10.
An image forming apparatus for recording images of each color by aligning scanning directions of the plurality of vibrating mirrors.

Images