JP2010066598A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner in which the shift of detection position of a synchronous detection depending on the scanning direction of a light beam which is reciprocally scanned with a deflection means is suppressed and the synchronous detection is performed without shift in detection positions between forward and returning scans. <P>SOLUTION: The optical scanner includes: a deflection means 106 which deflects the light beam emitted from a light source means and reciprocally scans a main scanning region; a scanning and imaging optical system 120 which guides the light beam from the deflection means onto a face to be scanned; light beam detection means (photodiodes or the like) PD+, PD- which detect the light beam from the deflection means, wherein one or more light detection means are disposed in a main scanning direction; and a plurality of light-receiving faces (PD for forward scan, PD for backward scan) which detect the light beam and are adjacent to each other in the main scanning direction. The width of the boundary of the adjacent light-receiving faces in the main scanning direction is denoted by Δw, the time in which the light beam passes through the boundary of the light-receiving faces is denoted by dt, the scanning frequency of the deflection means is denoted by fd, the effective scanning term rate of the image region is denoted by μ and the writing-in width of the main scan is denoted by W, the following relation is satisfied: Δw<W×dt/äμ/(2×fd)}×1,000. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical scanning device that guides and scans a light beam emitted from a light source means to a surface to be scanned, and an image forming apparatus including the optical scanning device, and more particularly, to a light beam detection means of the optical scanning device. The present invention relates to light amount control for selecting a light beam and detecting synchronization detection.

  In conventional optical scanning devices, polygon mirrors and galvanometer mirrors are used as deflecting means for scanning the light beam, but in order to achieve higher resolution images and high-speed printing, the polygon mirrors and the like are rotated at higher speeds. Therefore, the durability of the bearing, heat generation due to windage damage, and noise become problems, and there is a limit to high-speed scanning.

In contrast, in recent years, research on deflection means (for example, MEMS vibrating mirrors) using silicon micromachining is underway, and as disclosed in Patent Document 1 and Patent Document 2, the vibrating mirror and its axis are arranged on a Si substrate. A method in which the supporting torsion beam is integrally formed has been 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.
In addition, the housing that houses the optical scanning device can be thinned due to low vibration and almost no heat generation, and even if 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.
However, when a vibrating mirror is used, the resonance frequency changes with temperature, and the deflection angle changes due to changes in the spring constant of the torsion beam due to temperature changes, or changes in the viscous resistance of air due to atmospheric pressure. There is a problem that it ends up.
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.

By using the vibration mirror as a substitute for the polygon mirror as described above, noise and power consumption can be reduced, and an image forming apparatus suitable for the office environment can be provided.
In addition, the housing can be made thinner as the vibration is reduced, and the weight and cost can be reduced.
Patent Document 6 discloses a light beam property evaluation method and an evaluation device that can evaluate the depth of each property required for a light beam.
Japanese Patent No. 2924200 Japanese Patent No. 30111144 Japanese Patent No. 3445691 Japanese Patent No. 3543473 JP 2004-279947 A Japanese Patent Laid-Open No. 2000-9589 Japanese Patent No. 3594813

In recent years, in order to cope with further increase in speed and color in an image forming apparatus, a multi-beam method is used in which writing is performed by simultaneously scanning a plurality of light beams on one image carrier.
When reciprocating scanning writing is performed by the MEMS vibration mirror, the scanning beam is scanned from the center of the amplitude to the outside, passes through the light receiving surface of the light beam detecting means provided outside the image forming area, and reaches the top of the amplitude. The light beam is scanned in the reverse direction and passes again on the light receiving surface of the light beam detecting means.
Therefore, unlike the case where a polygon mirror is used as the conventional deflecting means, the light receiving surface of the light beam detecting means is traversed in the reverse direction in the forward scanning and the sub scanning, and only the width of the light receiving surface in the main scanning direction, The image height for detecting the light beam will shift.
For this reason, when a PD + and PD− synchronous detector (photodiode or the like) is installed as a light beam detection means at the position of the deflection angle θs on both sides in the main scanning direction outside the image forming area, The forward scanning time and the backward scanning time by the reciprocating scanning that passes through the image height 0 are measured in a section that is shifted in the image height direction by the width of the light receiving surface in the direction opposite to the traveling direction.

Based on this detection data, when adjusting the vibration mirror attitude control, writing start position, and writing conditions (pixel pitch, image frequency, etc.) for each reciprocating scan, always use the synchronization detector (PD). A residual is left by the width of the light receiving surface in the main scanning direction.
Further, even when the maximum amplitude is reached from the synchronization detector (PD) and returns to the synchronization detector (PD) again, although the same synchronization detector (PD) is received, the light received by the PD of the scanned light beam is received. Since the approach direction to the surface is reversed, a difference corresponding to the width of the light receiving surface is generated in the forward and return paths from the synchronous detector (PD) to the maximum amplitude.

  The present invention has been made in view of the above circumstances, and accurately detects the timing when the light beam scanned in the forward path and the backward path by the deflecting means (vibrating mirror) passes through the common boundary of the light beam detecting means. Therefore, it is possible to suppress the detection position shift of the synchronous detection due to the scanning direction of the light beam, and by obtaining detection signals from the insulated light receiving surfaces in the forward scan and the backward scan, respectively, the conventional light receiving surface width can be obtained. It is an object of the present invention to provide an optical scanning device capable of synchronous detection without displacement of the detection position of the minute, and further to provide an image forming device including the optical scanning device and capable of performing high-speed and good image formation. Is an issue.

In order to solve the above problems, the present invention employs the following solutions.
The first means of the present invention includes a light source means for emitting a light beam, a light source driving means for modulating and driving the light source means, and deflecting the light beam emitted from the light source means for reciprocating scanning in the main scanning region. A deflecting unit; a scanning imaging optical system that guides the light beam from the deflecting unit onto a surface to be scanned; and a light beam detecting unit that detects the light beam from the deflecting unit. In the optical scanning device, the light beam detecting means has a plurality of light receiving surfaces for detecting a light beam and has a light receiving surface adjacent to the main scanning direction. The width of the boundary between the light receiving surfaces adjacent in the direction is Δw [μm], the time for the light beam to pass through the boundary of the light receiving surface is dt [ns], the scanning frequency of the deflecting means is fd [Hz], and the effective image area Scanning period rate is μ, main driving When the writing width and W [mm],
Δw <W × dt / {μ / (2 × fd)} × 1000
It is set to satisfy the relational expression.

According to a second means of the present invention, in the optical scanning device of the first means, the width in the main scanning direction of the boundary between the adjacent light receiving surfaces is Δw [μm], and the main scanning beam of the light beam on the surface to be scanned is set. When the diameter is φm [μm]
Δw <φm × 0.125
The light receiving surface is arranged so as to satisfy the relational expression.
According to a third means of the present invention, in the optical scanning device of the first or second means, the light source means has a plurality of light emitting portions for emitting light beams, and the light source driving means is the light source means. A plurality of light emitting sections of the light source means are driven by the light source driving means when the light beam detecting means detects a light beam that is reciprocally scanned by the deflecting means and passes through the light receiving surface. By controlling the amount of emitted light, a light beam to be detected is selected and detected from a plurality of light beams.

  According to a fourth means of the present invention, in the optical scanning device according to any one of the first to third means, the light source means has a plurality of light emitting portions that emit light beams, and the light source driving means includes: A plurality of light emitting sections of the light source means are modulated and driven, the deflection means deflects the light beam emitted from the light source means to reciprocate the main scanning region, and the scanning imaging optical system is supplied from the deflection means. The light beam is guided onto the surface to be scanned, and the light beam detecting means detects the light beam from the deflecting means with one or more light receiving surfaces, and the maximum deflection angle of the reflecting surface of the deflecting means is When the light beam emitted from the light source means is larger than the incident angle to the reflecting surface of the deflecting means, the light source driving means is based on the detection signal detected by the light beam detecting means. Light emission control period for the light emitting part that is forcibly turned off And controlling the timing and duration.

  According to a fifth means of the present invention, in the optical scanning device according to any one of the first to fourth means, the deflection means is supported by a torsion beam, and deflects the light beam from the light source means to perform main scanning. It is a vibrating mirror that reciprocally scans an area.

According to a sixth means of the present invention, in the optical scanning device according to any one of the first to fifth means, the shift of the amplitude center of the deflection means calculated based on the detection signal detected by the light beam detection means. In accordance with the amount, the timing and time setting of the light emission amount control period by the light source driving means are controlled by the deflection control means.
According to a seventh means of the present invention, in the optical scanning device of any one of the first to fifth means, the maximum amplitude of the deflecting means is constant based on the detection signal detected by the light beam detecting means. It is characterized by controlling by a deflection control means.
Further, an eighth means of the present invention is the optical scanning device of any one of the first to fifth means, wherein the deflection frequency is calculated based on the detection signal detected by the light beam detecting means. Accordingly, the timing and time setting of the light emission amount control period by the light source driving means are controlled by the deflection control means.
Still further, a ninth means of the present invention is the optical scanning device of any one of the sixth to eighth means, wherein the deflection means is controlled by the deflection control means.

  The tenth means of the present invention is the image forming apparatus comprising at least one image carrier and at least one optical scanning device for scanning the at least one image carrier with a light beam including image information. As an optical scanning device, the optical scanning device of any one of the first to ninth means is provided.

In the optical scanning device of the first means of the present invention, the electrically isolated light receiving surfaces of the light beam detecting means are arranged adjacent to each other in the main scanning direction, and each of them is used as a light receiving surface exclusively for the forward path and for the backward path, By accurately detecting the timing at which the light beams scanned in the return path pass through a common boundary, it is possible to suppress the detection position shift of the synchronization detection due to the scanning direction of the light beams. In addition, by obtaining detection signals from the light receiving surfaces that are insulated in the forward scanning and the backward scanning, it is possible to perform synchronous detection without any detection position deviation corresponding to the width of the conventional light receiving surface.
Further, in the optical scanning device of the first means, the width of the boundary between the light receiving surfaces adjacent in the main scanning direction is Δw [μm], the time for the light beam to pass through the boundary of the light receiving surface is dt [ns], and the deflection means When the scanning frequency is fd [Hz], the effective scanning period rate of the image area is μ, and the main scanning writing width is W [mm],
Δw <W × dt / {μ / (2 × fd)} × 1000
The boundary of the light receiving surface at the time dt during which the light beam passes over the boundary of the light receiving surface, rather than the distance that the light beam is scanned in the image forming area per unit time. By setting the width Δw in the main scanning direction to be small, the detection accuracy of the synchronous detection of the light beam that scans the main scanning region can be made higher than the accuracy of the image forming region.

In the optical scanning device of the second means, when the width of the boundary between adjacent light receiving surfaces in the main scanning direction is Δw [μm] and the main scanning beam diameter of the light beam on the surface to be scanned is φm [μm],
Δw <φm × 0.125
The light receiving surface is arranged so as to satisfy the following relational expression, and the boundary width Δw between adjacent light receiving surfaces is set to 1/8 or less of the beam spot diameter φm of the main scanning, so that the detection position shift slightly due to the remaining boundary width. The accuracy of detecting a light beam spot position can be improved.

  In the optical scanning device of the third means, only the detection target light beam is emitted outside the image forming region by causing only the detection target light beam to emit light above the detection level and controlling the other light beams below the emission level. Can be captured by the light receiving surface for synchronous detection, and the light beam to be detected can be clearly detected. In addition, it is possible to individually set the write start position and write width for each of the plurality of light beams. Further, the vibration state of the deflecting means can be detected by detecting individual light beams, and posture control can be performed smoothly.

  In the optical scanning device of the fourth means, even when the maximum deflection angle of the deflecting means is larger than the incident angle of the image forming area, the light source means is also used in a section other than the synchronous detection section at the deflection angle exceeding the image forming area. By forcibly turning off the light emitting section, it is possible to suppress the inflow of ghost light other than the light beam to be detected to the light receiving surface.

  In the optical scanning device of the fifth means, by using a vibrating mirror supported by a torsion beam as the deflecting means, compared with the deflecting means using the conventional polygon scanner, low noise, low heat generation, and low power consumption. In particular, it is possible to solve the problem of image deterioration due to the temperature change of the optical element due to the heat generated from the polygon motor, and it is possible to realize a highly accurate drawing image.

  In the optical scanning device of the sixth means, the timing of the light emission amount control period by the light source driving means according to the shift amount of the amplitude center of the deflecting means calculated based on the detection signal detected by the light beam detecting means, and Since the time setting is controlled by the deflection control means, when the vibration state of the deflection means (vibrating mirror) fluctuates due to disturbances such as temperature and humidity fluctuations, the light beam is synchronized when the center of amplitude shifts in the image height direction. The approach image height to the light-receiving surface for detection, where the difference in the light-receiving surface width has occurred in the forward scan and the backward scan in the past, is placed in close proximity to the two light-receiving surfaces, each of the forward scan and the backward scan By assigning a dedicated light-receiving surface to each other, it becomes possible to detect the timing at which the light beam has passed through the boundary shared by both, and the shift amount of the amplitude center by the deflecting means (vibrating mirror) can be more appropriately It is possible to put out correction.

  In the optical scanning device of the seventh means, the deflection control means controls the deflection means so that the maximum amplitude of the deflection means becomes constant based on the detection signal detected by the light beam detection means. When the light beam passes through the light receiving surface of the beam detecting means, reaches the maximum amplitude and passes again through the light receiving surface of the light beam detecting means, the width of the light receiving surface is conventionally adjusted to the height of the light beam entering the light receiving surface by forward scanning and backward scanning. Deflection control means that the difference between the minute and minute is arranged so that the forward and backward scanning dedicated light receiving surfaces are adjacent and share a boundary, so that the maximum amplitude becomes constant with higher accuracy. Thus, the drive current value and scanning frequency of the deflecting means (vibrating mirror) can be controlled and corrected.

  In the optical scanning device of the eighth means, the timing and time setting of the light emission amount control period by the light source driving means are deflected according to the scanning frequency of the deflecting means calculated based on the detection signal detected by the light beam detecting means. Since it is controlled by the control means, the deviation of the detection position can be reduced by arranging the light receiving surfaces dedicated to the forward scanning and the backward scanning so as to share the boundary, and according to the scanning frequency of the deflection means. The light beam writing start position, the light emission timing, the amplitude width, and the like can be controlled.

  In the optical scanning device of the ninth means, in the optical scanning device of any one of the sixth to eighth means, the deflection means controls the scanning state of a desired light beam by controlling by the deflection control means. Can be maintained.

  Since the image forming apparatus of the tenth means includes the optical scanning apparatus of any one of the first to ninth means as the optical scanning device, when using the deflecting means for performing reciprocating scanning, In the backward scan, there was an error in the width of the light receiving surface of the light beam detecting means installed in the main scanning direction, but the forward scanning and the backward scanning are adjacent to each other so as to share the boundary. Thus, detection can be performed while suppressing the difference, and a higher-definition output image can be formed.

  The present invention relates to synchronous detection of a light beam emitted from a light source means and reciprocally scanned in a main scanning direction by a deflection means (vibrating mirror). In forward scanning and backward scanning, the light beam detecting means enters the light receiving surface. Are alternately reversed, so that the problem that the detection position of the scanned light beam is shifted by the width of the light receiving portion in the main scanning direction is solved. Adjacent by arranging the insulated light receiving surfaces adjacent to each other in the main scanning direction, assigning a dedicated light receiving surface for each of the forward scan and the backward scan, and arranging the light receiving surfaces adjacent to each other so as to share a boundary. The light beams passing through the boundary can be detected respectively.

As a result, in the conventional optical scanning device, the synchronization detector (light receiving element such as a photodiode (PD) or CCD) caused a detection position shift corresponding to the width of the light receiving surface in forward scanning and backward scanning. In the optical scanning device of the invention, the above-mentioned problem is caused by arranging a synchronous detector (light receiving element such as PD or CCD) having a light receiving surface for detecting each of forward scanning and backward scanning as a light beam detecting means. Can be eliminated. At present, the light receiving surfaces can be arranged at intervals of about 5 μm, and jaggy (jagged line) is 0.00435%, which satisfies the ideal jaggy.
Further, by arranging the dedicated light receiving surfaces adjacent to each other so as to share the boundary, the scanning beam can suppress the detection position shift due to the reciprocating scanning of the light receiving surface of the synchronous detector as the light beam detecting means. it can.

Hereinafter, the configuration, operation, and effects of the optical scanning device and the image forming apparatus according to the present invention will be described in detail based on the illustrated embodiments.
It should be noted that the detection position of the light beam reciprocally scanned by the deflecting means is shifted by the width of the light receiving surface of the light beam detecting means in forward scanning and backward scanning. An example of an optical scanning apparatus and an image forming apparatus in which the surface is switched between forward scanning and backward scanning, the light receiving surface is arranged so as to share a boundary close to each other, and detection position deviation is suppressed will be described with reference to the drawings.

FIG. 1 shows a configuration example of a main part of an image forming apparatus provided with an optical scanning device of a system (one-side scanning system) that scans four stations (latent image forming stations for each color) by a single deflecting means (vibrating mirror) 106. It is shown.
As shown in the figure, the optical scanning device that scans each photosensitive drum (image carrier) 101, 102, 103, 104, which is the surface to be scanned, is integrally formed, and the moving direction of the intermediate transfer belt 105 as a transfer body The light beams from the light source units 107 and 108 as light source means corresponding to the four photosensitive drums 101, 102, 103, and 104 arranged at equal intervals along By separating and guiding again, an image (latent image) is simultaneously formed.
Further, the light beams from the light source units 107 and 108 are deflected at a different incident angle in the sub-scanning direction to the oscillating mirror 106, whereby the light beams from the light source units 107 and 108 are collectively deflected. To scan.

The light source units 107 and 108 have light sources (for example, semiconductor lasers (LD)) for two stations arranged in the sub-scanning direction, adjusted so that the angle formed by the light beams from each light source is 2.5 °, and the vibrating mirror 106 is integrally supported by a reflecting surface 106 (vibrating mirror surface 441 of a vibrating mirror 460 shown in FIG. 12 described later) so as to intersect the sub-scanning direction.
In the present embodiment, the light source unit 107 tilts the light beam from the lower light source parallel to the light source unit 107 and the light beam from the upper light source by 2.5 ° with respect to the light emission axis of the light source unit 107, and the emission axis is main-scanned. It arrange | positions so that it may incline 1.25 degrees downward with respect to a plane.
On the other hand, the light source unit 108 tilts the light beam from the upper light source parallel to the emission axis of the light source unit 108 and the light beam from the lower light source by 2.5 °, and the emission axis is relative to the main scanning plane. And tilted upward by 1.25 °.

Further, each light source unit is arranged with its installation height changed in the sub-scanning direction so that the emission axes of the light source units 107 and 108 intersect the sub-scanning direction at the vibrating mirror surface 441.
That is, the light source unit 108 is disposed so as to be lower than the light source unit 107 in the sub-scanning direction, and the incident mirror 111 causes the sub-beams 201, 202, 203, and 204 to be aligned in a vertical line so that the beams 201, 202, 203, and 204 are aligned in a vertical line. The incident light is incident on the cylinder lens 113 at different heights in the scanning direction, and the incident angle in the main scanning direction is 22.5 ° (= α / 2 + θd) with respect to the normal line of the vibrating mirror 106. The light is incident on the mirror 106 so as to intersect the sub-scanning direction.
Each beam is converged in the sub-scanning direction in the vicinity of the vibrating mirror surface by the cylinder lens 113, and after deflection, is incident on the scanning lens 120 while increasing the interval so that the beams are separated from each other. The scanning 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 scanning lens 120, the lower beam 204 from the light source unit 108 is reflected by the folding mirror 126 and imaged in a spot shape on the photosensitive drum 101 via the toroidal lens 122. Then, a latent image based on yellow image information is formed as the first image forming station.
Further, the upper beam 203 from the light source unit 108 is reflected by the folding mirror 127 and forms a spot image on the photosensitive drum 102 via the toroidal lens 123 and the folding mirror 128 to serve as a second image forming station. A latent image based on magenta image information is formed.

The lower beam 202 from the light source unit 107 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 is cyan as a third image forming station. A latent image based on the image information is formed.
Further, the upper beam 201 from the light source unit 107 is reflected by the folding mirror 131 and 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. A latent image based on the black image information is formed.
The above components are integrally held in a single housing shown in FIG. 21, as will be described later.

  The light beam deflected by the oscillating mirror 106 passes through the side of the scanning lens 120 to the synchronization detection sensor (hereinafter also referred to as “synchronization detection PD” or “synchronization detector”) 138 as a light beam detection unit, and forms an image. The lens 139 is focused and incident, and a synchronization detection signal for each station is generated based on the detection signal. In FIG. 1, the synchronization detection sensor 138 and the imaging lens 139 are only shown on one side outside the image forming area of the photosensitive drum, which is the surface to be scanned, but as will be described later, synchronization detection is performed. The sensor 138 and the imaging lens 139 are installed on both sides outside the image forming area.

The exit roller portion (left end portion in FIG. 1) of the intermediate transfer belt 105 is provided with overlay accuracy detection means for detecting the overlay accuracy of each color image formed and superimposed at each station.
This overlay accuracy detecting 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. Done.
In the present embodiment, the overlay accuracy detecting means is composed of an LED element 154 for illumination, a photo sensor 155 for receiving reflected light, and a pair of condensing lenses 156, and is arranged at three positions on the left and right ends and the center of the image. Then, the detection time difference from the reference color black is read in accordance with the movement of the intermediate transfer belt 105.

  Here, FIG. 2 shows an example of a control system of the optical scanning device shown in FIG. As shown in FIG. 2, the optical scanning device includes a plurality of PDs 138 (photodiodes (PD +, PD−)) that detect a light beam deflected by the oscillating mirror 106 and scanned on the surface to be scanned (image surface). The configured light beam detection unit 302 and the light emitting units (LD light source units) of the light source units 107 and 108 in accordance with the timing at which the light beam passes through the light receiving surface of the PD (PD +, PD−) of the light beam detection unit 302. And the light source driving means 301 for turning on the light in a pulsed manner, and the pixel clock and count passed through the PD (PD +, PD−) for detecting the light beam on the light receiving surface in accordance with the timing of the light beam passing on the light receiving surface. Measuring means 303 and a deflection control means 304 for controlling the deflection of the oscillating mirror 106.

Hereinafter, an operation procedure of the optical scanning device having a light emission amount control period in which the semiconductor laser (LD) is forcibly turned off will be described. In order to simplify the description, the case where only the LD light source of the light source unit 107 is turned on will be described.
The light beam emitted from the LD light source of the light source unit 107 pulse-driven by the light source driving unit 301 is deflected and scanned by the vibrating mirror 106, and the light beam passes over the synchronous detection PD (PD +) which is the light beam detecting unit 302. When this is done, the value of the pixel counter in the light source driving means of the light beam is reset to zero. The LD light source can be pulse-driven by appropriately designating the write start position, end position, dot interval, etc. starting from the synchronization detection PD (PD +, PD−) installed on both sides of the scanned surface. A dot can be formed in a desired position and width.

  That is, the amplitude, phase, period, offset, and the like of the oscillating mirror 106 are calculated based on the signal detected by the synchronization detection PD, and the oscillating mirror 106 is controlled by the deflection control unit 304. The LD light source is driven and controlled by the light source driving unit 301 in accordance with the operating state of the vibrating mirror 106, and the LD light source is driven to pulse in accordance with the writing data in the image forming area.

In FIG. 2, as the light beam detection means 302, two synchronization detection PDs (PD +, PD−) are installed on both sides outside the image forming area to detect the scanning state of the reciprocated light beam and deflect it. A block configuration diagram of a control system in which the control unit 304 controls the oscillating mirror 106 and simultaneously modulates and drives the light beam by the light source driving unit 301 is shown.
To the synchronization detection sensor PD (PD +, PD−), the light beam deflected by the oscillating mirror 106 passes through the side of the scanning lens 120 and is focused and incident by the imaging lens 139. The detection signal Based on the above, a synchronization detection signal for each station is generated.

Conventionally, the relationship between the incident angle α from the light source unit 107 to the vibrating mirror surface and the swing angle (amplitude) θ0 of the vibrating mirror 106 is α> 2θ0, and the maximum deflection angle 2θmax is
2θmax = α + 2θ0
However, in order to suppress the effective scanning rate (θd / θ0) to a predetermined value or less, which is 0.6 or less in this embodiment, in this embodiment,
θ0 ≧ α / 2> θd
θ0 ≧ θs> θd
(Here, θd is an effective deflection angle for scanning the photosensitive member, and θs is a deflection angle at the time of synchronous detection).
The incident angle α of the light beam from the LD light source of the light source unit 107 to the vibrating mirror surface is set so as to satisfy the following relationship.
Specifically, θ0 = 25 °, θd = 15 °, α = 45 °, and θs = 18 °.
Note that the synchronization detection sensor PD may be arranged so that θs> α / 2.

  FIG. 2 shows an example in which the amplitude center of the oscillating mirror 106 does not coincide with the optical axis of the scanning lens 120, that is, an example in which the amplitude center is shifted to the light source side and the amplitude is shifted. It is arranged so as to coincide with the optical axis, and the surface shape of the scanning lens or toroidal lens is a curved surface shape symmetrical along the main scanning direction.

As described above, the vibrating mirror surface is deformed in a wave shape with the reciprocating vibration. The amount of deformation δ becomes maximum when the amplitude is θ0, and there is a tendency that the amount of change increases in proportion to the change from the deflection angle 0 to θ0.
That is, since the deflection angle θd for scanning the scanning region is determined by the angle of view of the scanning lens 120, the effective scanning rate (θd / θ0), which is the ratio of the deflection angle θd for scanning the scanning region to the amplitude θ0, is smaller. Is less susceptible to mirror deformation.

However, in order to increase the amplitude θ0, it is necessary to reduce the mass of the mirror substrate, and conversely, if the mirror substrate is made thinner, the amount of deformation increases.
In this embodiment, the effective scanning rate (θd / θ0) is set so that the angular velocity of the oscillating mirror 106 is within a relatively constant range of the deflection angle, and the deflection angle θd for scanning the scanned region is 60% or less of the amplitude θ0. By doing so, deformation is suppressed.
On the other hand, when the incident angle α is increased, it is easily affected by dynamic surface deformation. Specifically, as shown in FIG. 2, the maximum amplitude 2θ0 = 50 °, the incident angle α = 45 °, the scanning angle 2θd = 30 °, and the synchronization detection angle 2θs = 36 °.

Here, as shown in FIG. 2, the synchronization detection PD (PD + and PD−), which is the light beam detection means 302, is installed on the surface to be scanned (image plane), and the timing at which the light beam passes over the synchronization detection PD is monitored. By doing so, it is possible to grasp the vibration state (phase, period, amount of shift of the center of vibration, magnification error, etc.) of the vibration mirror 106.
That is, the start position of the light emission amount control period in which the vibration state of the vibrating mirror 106 is detected by the pixel clock count measuring unit 303 that counts the pixel clock from the PD passage and is forcibly turned off in the same manner as the synchronous detection of the write start position, Light source drive control is performed via the light source drive unit 301 so as to appropriately control the end position and the section width.
Then, the vibration state of the vibration mirror 106 is sent to the deflection control means 304 and controlled so that the vibration mirror performs a desired vibration according to control parameters such as a drive voltage and a vibration frequency.

In the optical scanning apparatus of the present embodiment having the configuration shown in FIGS. 1 and 2, the light source units 107 and 108 for emitting light beams, and the light source driving means 201 for modulating and driving the light source units 107 and 108 are provided. The oscillating mirror 106 that deflects the light beams emitted from the light source units 107 and 108 to reciprocately scan the main scanning region, and guides the light beams from the oscillating mirror 106 onto the scanned surfaces (photosensitive drums) 101 to 104. Scanning imaging optical systems 120 and 122 to 130, and a light beam detection unit 302 that detects a light beam from the vibrating mirror 106 with a synchronization detection sensor (PD + and PD−) 138, and a synchronization detection sensor of the light beam detection unit 302. One or more (PD + and PD−) 138 are arranged in the main scanning direction, and a synchronization detection sensor (PD + and PD−) 138 of the light beam detecting means 302 is provided. , Which has a plurality of light receiving surfaces for detecting the light beam, and a light receiving surface adjacent to the main scanning direction (PD for outward later, PD for backward). The width of the boundary between the light receiving surfaces adjacent in the main scanning direction (forward path PD, return path PD) is Δw [μm], the time for the light beam to pass through the boundary of the light receiving surface is dt [ns], and the vibrating mirror 106 When the scanning frequency is fd [Hz], the effective scanning period rate of the image area is μ, and the main scanning writing width is W [mm],
Δw <W × dt / {μ / (2 × fd)} × 1000
Is set so as to satisfy the relational expression.

In the optical scanning device of the present embodiment, the width in the main scanning direction of the boundary between adjacent light receiving surfaces (the forward path PD and the backward path PD described later) is Δw [μm], and the light beam on the scanned surface is When the main scanning beam diameter is φm [μm],
Δw <φm × 0.125
The light receiving surface is arranged so as to satisfy the relational expression.

  Furthermore, the light source units 107 and 108 have a plurality of light emitting units (LD light sources) that emit light beams, and the light source driving means 301 modulates and drives the plurality of light emitting units (LD light sources) of the light source units 107 and 108 to generate light. When the light detection unit (PD +, PD−) 138 of the beam detection unit 302 detects a light beam that is reciprocally scanned by the oscillating mirror 106 and passes through the light receiving surface, the light source driving unit 301 uses the plurality of light source units 107, 108. The amount of light emitted from the light emitting unit (LD light source) is controlled to select and detect a light beam to be detected from a plurality of light beams.

  Furthermore, in the optical scanning device of the present embodiment, the maximum deflection angle 2θ0 of the mirror surface of the vibrating mirror 106 is larger than the incident angle α of the light beam emitted from the light source units 107 and 108 to the mirror surface of the vibrating mirror 106. If larger, the light source driving means 301 is a light emitting unit (LD light source) that forcibly turns off the light source units 107 and 108 based on the detection signal detected by the synchronization detection sensor (PD +, PD−) 138 of the light beam detecting means 302. ) To control the timing and duration of the light emission amount control period.

In the optical scanning device of the present embodiment, the amplitude center shift amount of the oscillating mirror 106 calculated based on the detection signal detected by the synchronization detection sensor (PD +, PD−) 138 of the light beam detection unit 302 is determined. The deflection control unit 304 controls the timing and time setting of the light emission amount control period by the light source driving unit 301.
Further, in the optical scanning device of the present embodiment, deflection is performed so that the maximum amplitude of the oscillating mirror 106 is constant based on the detection signal detected by the synchronization detection sensor (PD +, PD−) 138 of the light beam detection means 302. Control is performed by the control means 304.
Further, in the optical scanning device of the present embodiment, the light source is selected according to the scanning frequency of the oscillating mirror 106 calculated based on the detection signal detected by the synchronization detection sensor (PD +, PD−) 138 of the light beam detection means 302. The deflection control means 304 controls the timing and time setting of the light emission amount control period by the drive means 301.
Note that at least one of the above-described controls is executed, and the vibrating mirror 106 is controlled by the deflection control means 304.

  Next, differences between synchronization detection in the conventional optical scanning device and synchronization detection in the optical scanning device of the present embodiment will be described.

3 and 4 show an example of conventional synchronization detection.
FIG. 3 shows the relationship between the light beam reciprocally scanned by the vibration mirror, the installation position of the conventional synchronization detection PD (PD +, PD−), and the detection signal of the PD (PD +, PD−) in the forward path and the return path. FIG.
The left-to-right scanning direction in FIG. 3 is the forward path, the right-to-left scanning direction is the forward path, and the width of the synchronous detection light-receiving surface in the main scanning direction is dw [mm]. Since the outward light beam enters the synchronization detection PD (PD + and PD−) from the left side, the detection signal is on the left side of each synchronization detection as indicated by the solid arrow.
On the other hand, the light beam in the return path enters from the right side of the light receiving surface of the synchronization detection PD (PD + and PD−), so that the PD detection signal in the return path has a light beam on the right side of dw from the forward path as indicated by the dashed arrow. When it reaches, the detection signal rises. Thus, since the scanning direction of the light beam is reversed in the forward path and the backward path, the light beam at a location shifted by the light receiving surface width dw of the synchronization detection PD is detected.

For this reason, as shown in FIG. 4, the forward scanning time T1 is a scanning time of the section of the light receiving surface width dw minus the image height, and the backward scanning time T2 is conversely the light receiving surface width dw plus the image height side. The scanning time is in the range.
Since the vibration mirror does not necessarily have the center of amplitude at the intermediate point between PD + and PD−, the attitude control of the vibration mirror and the light beam emission conditions are performed in a state where a residual of the light receiving surface width dw is always generated. Therefore, it is difficult to appropriately control the desired value.

For example, when the scanning frequency fd of the vibrating mirror is 2500 Hz, the image height is ± 120 mm when the maximum deflection angle 2θ0 = 30 °, and the image height is ± 100 mm when the synchronization detection is ± 2θs = 25 °, the image height is 0 If T is the time required to reach the deflection angle θ from
T = (1 / 2πfd) × sin ⁻¹ (θ / θ0)
When the time to pass the image height of 100 mm is T100 and the time to the image height of 101 mm is T101,
T100 = 65.2554 [μs]
T101 = 66.1782 [μs]
If the time required for passing between synchronous detections is twice as long as T100, the time for scanning the light beam with the light receiving surface width dw = 1 mm is 0.9228 [μs], and the ratio of the error due to the light receiving surface width Is
0.9228 / (2 × T100) = 0.707 [%].
This greatly exceeds the allowable limit of jaggy (jagged lines) of about 0.01 [%], and has a great influence on image quality.

FIG. 5 shows an embodiment of the present invention.
As shown in FIG. 5 (a), the light receiving surfaces of the synchronization detection PD + and the synchronization detection PD- are divided into the forward path PD and the backward path PD, and are arranged so as to be adjacent as much as possible. Can be made into a shape. At that time, the adjacent forward PD and the backward PD are electrically insulated from each other, and output detection signals independently detecting the scanning of the light beam.
Further, as shown in FIG. 5B, by arranging photodiodes or CCD cameras as light receiving elements as adjacent as possible in the main scanning direction, the boundary shared between the forward PD and the backward PD is narrowed. It is possible.

  At present, it is possible to arrange them on the same plane at intervals of about several μm, and the interval between the return PD and the forward PD sharing the boundary adjacent to the light beam detection means is Δw = 5 [μm. ], The time taken for the light beam to pass is 0.0458 [μs], and the error rate due to the boundary width is within 0.00435 [%]. Based on the detection measurement data, correction of the beam spot position by the light beam, correction of the writing start position, and feedback to the attitude control of the vibrating mirror can be appropriately performed.

  As a result, when the forward scanning is performed, detection is performed by the rightward traveling PD, and conversely, when the backward scanning is performed, the light beam is detected by the leftward traveling PD in the drawing, so that a common boundary can be detected. The timing at which the beam passes can be detected, and the detection signals for the forward path and the return path can be detected at the timing when the image height has passed through substantially the same.

FIG. 6 shows a schematic diagram of detection results of the forward scanning time T1 and the backward scanning time T2 improved by the present invention.
FIG. 7 shows a graph of a vibrating mirror (vertical deflection angle, horizontal axis time) when the synchronization detection PD + and the synchronization detection PD− are installed on both outer sides of the image forming area, and a time chart regarding the LD lighting timing. .
The thick line part (± 2θd) of the sine wave curve of the oscillating mirror corresponds to the image forming area, and the synchronization detection PD + and the synchronization detection PD− are installed on both outer sides (± 2θs) to detect the scanning state of the light beam. ing. Since the light source means is provided on the PD + side, the return light is generated when the light beam is scanned on the PD + side. In the vicinity of the incident angle α from the light source means to the surface of the oscillating mirror, the oscillation angle of the oscillating mirror is θs to θ0 (scanning angles 2θs to 2θ0). Therefore, it is possible to prevent the oscillation and light emission of the semiconductor laser constituting the light source means from becoming unstable.

FIG. 8 shows a schematic diagram when the vibration state of the vibration mirror changes. FIG. 8A shows a case where the amplitude of the vibrating mirror is larger on the broken line than on the solid line. Times A and B from when the scanned light beam passes through the synchronization detection PD (PD +, PD−) installed on both sides outside the image area to reach the maximum image height and pass through the synchronization detection again are as follows. The A and B sides change with the same tendency. This is a relationship proportional to the tendency of the amplitude of the vibrating mirror. Therefore, by setting a relational expression between the change in the amplitude of the vibrating mirror and the installation position of the synchronous detection PD in advance in a database, an appropriate light emission amount control period for forcibly turning off according to the amplitude status of the vibrating mirror is set. Can do.
Specifically, when the light source means is arranged in the direction of the A side, the time for the light beam to pass through the synchronous detection increases in the broken line, and the time for the light beam to reach the incident angle α is shortened. It is necessary to advance the forced turn-off time. Conversely, since the time for the light beam to return from the maximum amplitude and reach the incident angle α again is delayed, it is necessary to delay the end of the light emission amount control period during which the light is forcibly turned off.

FIG. 8B shows a case where the amplitude center at the image plane position of the vibrating mirror is shifted to the + image height side. + In the synchronous detection PD + on the image height side, the time A from when the scanning beam passes through to reach the maximum image height and back again increases, but in the synchronous detection PD− on the opposite side, the maximum image height is reached. On the contrary, the time B until returning again decreases.
Thus, even when the amplitude center of the vibration mirror is shifted to one side, the relational expression of the time when the light beam is scanned and passed through the synchronization detection PD in the installation relationship between the amplitude center of the vibration mirror and the synchronization detection PD is a database. By making it, it is possible to set a desired light emission amount control period during which the light is forcibly turned off.

9 to 11, the time t <b> 1 until the light beam scanned by the vibrating mirror passes through the synchronization detection PD installed on the + image height side, reaches the maximum amplitude, and returns again, and the synchronization detection PD is scanned. Similarly, an example of the relationship with the time t2 until the light beam passes through the synchronization detection PD will be shown.
In FIG. 9, since the deflection angle of the vibrating mirror is larger than the solid line by the broken line, t1 ′ is larger than t1 of the solid line, but since the period of the vibrating mirror is not changed, t2 and t2 ′ are does not change. Therefore, by measuring t1 and t2, the fluctuation of the swing angle of the vibrating mirror can be measured, and the light source driving means drives and modulates the light source so as to change the setting of the light emission amount control period forcibly turning off correspondingly. can do.

FIG. 10 shows a case where the amplitude center of the vibrating mirror is shifted to the image height + side. As in FIG. 9A, the period of the oscillating mirror does not change, so t2 and t2 ′ do not vary, but t1 ′ is larger than t1 that is shifted to the image height + side by the broken line. However, since the synchronization detection PD is only on one side (image height + side), it cannot be measured that the solid line is larger than the broken line on the opposite side, and it is distinguished whether the amplitude center of the vibrating mirror has shifted or the amplitude has increased. I can't. In order to observe the amplitude fluctuation of the vibration mirror and the state of the vibration center, it is necessary to install the synchronization detection PD on both outer sides of the image area.
When the synchronization detection PD is installed on both outer sides of the image area, a desired light emission amount control period during which the forced turn-off is performed can be calculated from the scanning state of the vibrating mirror obtained by the synchronization detection PD.

  FIG. 11 shows a case where the period is changed. In this case, the broken lines t1 'and t2' are larger than the solid lines t1 and t2 by the increase of the period. Similarly, from this measurement result, pulse modulation driving is performed by the light source driving means so as to increase the period and the length of the light emission amount control period during which the light is forcibly turned off.

Next, a configuration example of a vibrating mirror used in the deflecting unit 106 of the optical scanning device in this embodiment will be described with reference to FIG. 12A is a plan view of the vibration mirror, FIG. 12B is a plan view of the back surface of the vibration mirror unit, FIG. 12C is a sectional view of the vibration mirror unit, and FIG. 12D is an exploded perspective view of the vibration mirror module. In this embodiment, an example of an electromagnetic drive system will be described as a method for generating the rotational torque of the vibrating mirror.
As shown in the drawing, the movable mirror 441 that forms the vibration mirror surface of the vibration mirror 460 is pivotally supported by a torsion beam 442, and as described later, is manufactured by etching through a single Si substrate, A vibration mirror substrate 440 is configured as a unit that is mounted on the mounting substrate 448 and integrally includes the vibration mirror.

  In this embodiment, a module is shown in which a pair of vibrating mirror substrates 440 are integrally supported back to back. This back-to-back configuration uses the one corresponding to the “opposite scanning method”, and in this embodiment, the “one-side scanning method” is exemplified as described above. It is unnecessary. Of course, a configuration dedicated to the “single-side scanning method” that supports only the single vibrating mirror substrate 440 may be used.

The support member 445 is formed of a 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 the mirror surface is at a predetermined angle with respect to the main scanning direction. Here, an edge in which metal terminal groups are arranged so that a positioning portion 451 for positioning so as to be inclined by 22.5 ° and a wiring terminal 455 formed on one side of the mounting substrate 448 of the vibration mirror substrate 440 are in contact with each other at the time of mounting. The connector portion 452 is integrally formed.
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 constituting a drive circuit for the vibration mirror, and power and control signals are input / output through the connector 454.

  The vibrating mirror 460 includes a movable part that forms a mirror surface 441 on the surface and forms a vibrator, a torsion beam 442 that supports the rotating part, and a frame 447 that forms a support part. The Si substrate is cut out by etching. Form.

In this embodiment, two substrates of 60 μm and 140 μm called SOI substrates are manufactured using a wafer 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, and then the vibrating mirror surface 441 and the frame 447 are left by anisotropic etching such as KOH from the surface side of the 60 μm substrate (first substrate) 462. The other part is penetrated to the oxide film, and finally, the oxide film around the movable part is removed and separated to form the structure of the vibrating mirror.

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 vapor-deposited on the surface side of the 60 μm substrate 462 to form a reflective surface, and on the surface side of the 140 μm substrate 461, a terminal 464 wired with a coil pattern 463 and a torsion beam with a copper thin film, and for trimming Patch 465 is 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 (not shown) on which the vibration mirror 460 is mounted and a yoke 470 formed so as to surround the vibration mirror are provided. 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 with the mirror surface facing up, and a Lorentz force is generated on each side parallel to the rotation axis of the coil pattern 463 by passing an electric current between the terminals 464, and the torsion beam 442 is twisted. Then, a rotational torque T for rotating the vibrating mirror surface (movable mirror) 441 is generated, and when the current is turned off, the vibration mirror surface (movable 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 brought close to the natural frequency of the primary vibration mode with the torsion beam 442 as the rotation axis of the structure constituting the vibrating mirror, the so-called resonance frequency f0, the amplitude is excited and a large deflection angle is obtained. Can be obtained.
Therefore, normally, the scanning frequency fd is controlled so as to be set or followed in accordance with the resonance frequency f0. However, as described above, the resonance frequency f0 is the moment of inertia of the vibrator constituting the vibration mirror. Therefore, if there is a variation in the dimensional accuracy of the finished product, a difference occurs between individuals, making it difficult to align the scanning frequencies fd of the vibrating mirrors.

The variation of the resonance frequency f0 is about ± 200 Hz depending on the process capability. For example, when the scanning frequency fd = 2 kHz, a scanning line pitch shift corresponding to 1/10 line occurs. When the A4 size is output, a magnification shift of several tens of mm occurs at the paper edge.
For this reason, those having similar resonance frequencies f0 are ranked by sorting, and the scanning frequency fd is selected and set according to each rank. However, if the resonance frequency f0 varies greatly, the number of ranks increases. Therefore, the number of options for the driving circuit of the vibrating mirror and the scanning frequency fd must be increased, so that the production efficiency is low, and it is necessary to replace the vibrating mirror with the same rank when performing replacement.

Therefore, in this embodiment, the inertia moment I is adjusted by gradually cutting the mass of the movable part by cutting the patch 465 formed on the back side of the movable part with a carbon dioxide laser etc. before mounting on the mounting board. However, even if there is a dimensional difference between individuals, the resonance frequency f0 is adjusted so as to fall within ± 50 Hz so that the resonance frequencies f0 substantially coincide with each other.
A fixed scanning frequency fd is set within the ranked frequency bands regardless of the resonance frequency f0.

FIG. 13 is a block diagram illustrating a configuration example of a light source driving circuit (light source driving unit) that drives a light source (LD) and a vibrating mirror driving circuit (deflection control unit) that swings the vibrating mirror 106 (460). The light source drive circuit includes a light source drive unit 604 that drives a light source (LD), a writing control unit 605, a pixel clock generation unit 606, and the like, and the oscillating mirror drive circuit includes a drive control unit (drive pulse generation unit / PLL circuit). 601, a gain adjustment unit 602, a movable mirror drive unit 603, an amplitude calculation unit 607, and the like.
As described above, the planar coil formed on the back side of the oscillating mirror is applied with an AC voltage or a pulse wave voltage so that the direction of current flow is switched alternately, so that the deflection angle θ is constant. Adjust the gain of the current to flow through and reciprocate.

FIG. 14 shows the relationship between the frequency f for switching the direction of current flowing through the planar coil of the oscillating mirror and the deflection angle θ. Generally, the frequency characteristic has a peak at the resonance frequency f0, and if the scanning frequency fd is made to coincide with the resonance frequency f0, the deflection angle can be maximized, but the deflection angle changes steeply near the resonance frequency.
Therefore, initially, the drive frequency applied to the fixed electrode can be set to match the resonance frequency in the drive control unit (drive circuits 601 to 603, 607) of the vibration mirror, but the spring constant associated with the temperature change can be set. When the resonance frequency fluctuates due to a change or the like, the deflection angle is drastically reduced, and there is a drawback 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, the deflection angle θ is determined by the time difference between the detection signal detected at the time of backward scanning and the detection signal detected at the time of forward scanning in the synchronous detection sensor 138 provided at the start end of the scanning region. It is detected and controlled so that the deflection angle θ is constant.
As a result, even when temperature fluctuations occur during measurement, the deflection angle θ can be kept constant, and the linear velocity of the light beam on the image plane can be kept substantially constant.

As shown in FIG. 15, since the oscillating mirror is resonantly oscillated, 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
It becomes.
If the synchronization detection sensor 138 detects a beam having a scanning angle corresponding to 2θs, a detection signal is generated between forward scanning and backward 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 this period, the light emission part (LD light source) is prohibited from emitting light. 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. 16, 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 changed with respect to time. 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.
In addition, it is possible to form a high-quality image with less positional deviation by specifying an appropriate writing start position by two-point synchronization and controlling the position and interval of pixels in accordance with the operating state of the vibrating mirror due to disturbance. it can.

  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. Further, as described above, since the center of amplitude of the vibrating mirror and the optical axis do not coincide with each other, 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 changed 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)
The light emission source may be pulse-modulated so as to be determined based on the relational expression

FIG. 17 is a block diagram of a drive circuit for modulating a semiconductor laser that is a light emitting source.
Image data is temporarily stored in the frame memory, read out sequentially to the image processing unit, and pixel data for each line is formed according to the matrix pattern corresponding to the halftone while referring to the relationship before and after, corresponding to each light source Transferred to the line buffer.
The write control circuit is read out from the line buffer using the synchronization detection signal as a trigger, and modulates independently.

Next, a clock generator for modulating each light emitting point will be described. The counter counts the high-frequency clock VCLK generated by the high-frequency clock generation circuit, and the comparison circuit gives this count value, a preset value L set in advance based on the duty ratio, and the transition timing of the pixel clock from the outside. . The phase data H that indicates the phase shift amount is compared, and when the count value matches the set value L, the control signal L that instructs the falling edge of the pixel clock PCLK is A control signal h for instructing the rising edge of 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. In this embodiment, 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.

FIG. 18 is a diagram illustrating 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. 19 shows the correction amount of the main scanning position in each pixel according to the main scanning position when modulated at a single frequency. A plurality of main scanning areas, in this embodiment, the main scanning area is divided into eight areas, and approximated by a polygonal line, so that the main scanning position deviation is zero at the boundary of each area, and the number of phase shifts is set for each area. Set and correct 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 the pixel clock fc, the total phase difference Δt uses the number of phase shifts Ni / ni,
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.

  The divided region widths 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.

  FIG. 20 is a diagram schematically showing the state of reflected light when the reflecting surface of the oscillating mirror is deformed. FIG. 20A is a case where the reflecting surface of the oscillating mirror is deformed by δ around the rotation axis. Indicates. When the reflecting surface 441 of the oscillating mirror is not deformed as shown in FIG. 20B, the collimated light beam remains in a parallel state after being deflected by the oscillating mirror. When the reflecting surface 441 of the oscillating mirror is convexly deformed as shown in FIG. 20 (c), the parallel collimated light beam is deflected by the oscillating mirror and then diffused, and is reflected on the image plane. It causes image deterioration such as beam diameter thickening. In addition, since the return light reflected by the oscillating mirror also returns to the light source in a range wider than the incident angle α, the APC is set when the light emission amount control period forcibly turning off is set wide or when the light cannot be turned off. By not performing the control, stable oscillation light emission of the semiconductor laser can be performed.

Therefore, when deformation on the reflecting surface of the vibrating mirror is predicted in advance, a substantially constant beam diameter can be obtained by applying pulse modulation driving for correcting beam thickness to the light source unit.
In addition, in order to perform correction in real time, it is necessary to provide a calculation unit that calculates an appropriate pulse drive correction method from fluctuations in the passage time interval of the light beam in synchronous detection and information on the beam profile obtained on the detection surface. There is. Similarly, it is necessary to provide a calculation unit that calculates an appropriate pulse drive correction method for the start, end position, and period of the light emission amount control period that is simultaneously forcibly turned off.

Next, FIG. 21 shows a configuration example of an optical housing of the optical scanning device.
The oscillating mirror module 253 (corresponding to the oscillating mirror 106 in FIG. 1) is mounted on an optical housing integrally formed with a side wall 257 so as to surround the oscillating mirror module 253, and the upper end edge of the side wall 257 is covered with an upper cover. By sealing with 258 and blocking from the outside air, a change in amplitude due to the convection of the outside air is prevented. A flat transmission window 259 is provided in the opening of the side wall through which the light beam enters and exits.
In FIG. 21, reference numeral 250 denotes a housing body, 252 denotes a light source unit (corresponding to the light source unit 108 in FIG. 1), 254 denotes a scanning lens (corresponding to the scanning lens 120 in FIG. 1), and 255 denotes a beam passage frame. Is shown.

Next, FIG. 22 shows a configuration example of an image forming apparatus equipped with the optical scanning device 900 shown in FIG.
In this image forming apparatus, four image forming stations corresponding to yellow, magenta, cyan, and black are arranged in parallel in the moving direction of the intermediate transfer belt 906 (corresponding to the intermediate transfer belt 105 in FIG. 1). The black image forming station will be described as an example. Around the photosensitive drum 901 (corresponding to the black photosensitive drum 104 in FIG. 1), a charging charger 902 for charging the photosensitive drum 901 to a high voltage, A developing device 904 that attaches the toner charged by the developing roller 903 to the electrostatic latent image recorded by the optical scanning device 900 and visualizes it, and a cleaning device 905 that scrapes and stores the toner remaining on the photosensitive drum 901. Has been placed. The configuration around the photosensitive drum of the other image forming stations is the same, and each image forming station has basically the same configuration except that the toner color is different.

  On the photosensitive drum of each image forming station, image recording is performed every two lines in one cycle by reciprocating scanning of the vibrating mirror 106 of the optical scanning device 900, and an electrostatic latent image is formed. The electrostatic latent image on each photoconductor drum is visualized with toner of each color of the developing device, and yellow, magenta, cyan, and black toner images are formed on each photoconductor drum. The yellow, magenta, cyan, and black toner images on the respective photosensitive drums are sequentially transferred onto the intermediate transfer belt 906 at appropriate timing, and are superimposed to form a color image.

  On the other hand, the recording paper S as a recording medium is supplied from a paper supply tray 907 by a paper supply roller 908, and is sent out by a registration roller pair 909 in accordance with the recording start timing in the sub-scanning direction. The toner image is transferred from the intermediate transfer belt 906 to the recording paper S by the transfer charger 910. Thereafter, the toner image transferred to the recording sheet S is fixed by the fixing device 911, and the recording sheet S after fixing is discharged to the discharge tray 913 by the discharge roller pair 912.

The embodiments of the optical scanning device and the image forming apparatus according to the present invention have been described above. However, according to the present invention, the following operational effects can be obtained.
The direction in which the light beam scanned by the deflecting means (vibrating mirror) 106 that reciprocally scans the main scanning region passes through the light receiving surface of the synchronization detection sensor (PD, CCD, etc.) 138 of the light beam detecting means 302 is determined by the vibrating mirror. Since the scanning direction is alternately changed in accordance with the amplitude of 106, the position where the light beam passes over the synchronization detection sensor 138 is changed by the width of the light receiving surface, and synchronization detection cannot be performed with high accuracy. Therefore, in the present invention, the synchronization detection sensor 138 has a plurality of light receiving surfaces adjacent to each other in the main scanning direction, and a dedicated light receiving surface (outward PD, backward PD) is arranged for each of the forward scanning and the backward scanning. By accurately detecting the timing at which the light beams scanned in the forward path and the backward path pass through the common boundary, it is possible to perform good synchronization detection without problems such as jaggies.
Further, by setting the detection width of the forward PD and the backward PD of the synchronization detection sensor 138 of the light beam detecting unit 302 to be smaller than the scanning amount per unit time in the image forming area, By increasing the accuracy of the detection means rather than the accuracy, it is possible to ensure the accuracy as the detection means at the time of light beam emission conditions and amplitude control of the vibrating mirror.

  In the optical scanning device according to the present invention, the forward and backward light receiving surfaces (the forward PD and the backward PD) are adjacent to each other to share the boundary, and thereby the width Δw of the boundary between the adjacent light receiving surfaces is subjected to main scanning. By setting the beam spot diameter to 1/8 or less of the beam spot diameter, the accuracy of the synchronization detection can be improved to a level of 1/8 or less of the beam spot diameter of the light beam passing through the synchronization detection. Can be at a level that does not matter. Even if the main scanning beam spot diameter is set to 80 μm, an error of about 10 μm occurs, and the beam spot position can be sufficiently detected.

  Furthermore, in the optical scanning device of the present invention, the plurality of light emitting units (LD light sources) are sequentially driven and scanned, and APC driving is performed, so that the light source of the light source is not affected by the return light from other light emitting units. Stable oscillation light emission is possible. Similarly, for synchronization detection, a light beam can be detected for each detection target.

  Furthermore, in the optical scanning device of the present invention, when a plurality of light emitting units (LD light sources) are provided, each of the light beams emitted from the light emitting unit is forcibly turned off when returning to other light emitting units. By providing a light emission amount control period or a light emission amount control period that suppresses the drive current to a predetermined value or less, appropriate APC control is possible without being affected by the return light from other light emitting units, and a stable semiconductor laser Oscillation light emission can be performed.

  Further, in the optical scanning device of the present invention, as the deflecting means 106, reciprocating scanning is performed by a vibrating mirror supported by a torsion beam, thereby realizing low heat generation, low noise, and low power consumption as compared with a polygon mirror or the like.

Further, in the optical scanning device according to the present invention, scanning by disturbance of the oscillating mirror or continuous driving is performed according to the shift amount of the amplitude center of the oscillating mirror calculated based on the detection signals of the light beams provided on both sides outside the image area. The light emission amount control period or the drive current forcibly turned off due to the frequency fluctuation can be appropriately set so that the light emission amount control period or the drive current is suppressed to a predetermined value or less, the influence of the return light is suppressed, and the semiconductor laser High-quality images can be formed on the image carrier.
Also, when the amplitude center of the oscillating mirror is moved, it can be determined by comparing the time difference between the two sides of the image height ± either side of the image height. The light emission amount control period can be appropriately controlled so as to suppress the light emission to a predetermined value or less.

  Furthermore, in the optical scanning device of the present invention, the deflection control means controls the maximum amplitude to be constant based on the detection signal of the scanned light beam, whereby the fluctuation of the maximum deflection angle due to disturbance of the vibrating mirror or continuous drive. Even in the case of occurrence of the occurrence of the problem, since the adjustment can be made so that the desired maximum amplitude is obtained, the light beam can be stably scanned, and a high-quality image can be formed on the image carrier.

Furthermore, in the optical scanning device of the present invention, by changing the timing and time setting according to the scanning frequency calculated based on the detection signal of the scanned light beam, it is possible to cause the disturbance of the vibrating mirror or the fluctuation of the scanning frequency due to continuous driving. The light emission amount control period or the drive current that has been forced to be turned off or the drive current can be appropriately reset so as to suppress the drive current to a predetermined value or less. An image can be formed on the image carrier.
Further, by combining the above control methods, a desired light beam scanning state can be realized.

  In the image forming apparatus of the present invention, since the above-described optical scanning device is provided, a high-quality image can be formed by a stable light source that is not affected by the return light, so color misregistration and color unevenness are reduced. High-quality images can be formed.

1 is a schematic perspective view illustrating an exemplary configuration of a main part of an image forming apparatus including an optical scanning device according to an embodiment of the present invention. It is a figure which shows an example of the control system of the optical scanning device shown in FIG. It is a figure which shows the relationship between the light beam reciprocated by a vibration mirror, the installation position of conventional synchronous detection PD (PD +, PD-), and the detection signal of PD (PD +, PD-) in an outward path and a return path. It is a figure which shows the change of the image height by the detection signal by the conventional synchronous detection PD (PD +, PD-) of FIG. 3, and the deflection scanning of a vibration mirror. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows one Example of this invention, (a) is the light beam reciprocated by a vibrating mirror, the installation position of synchronous detection PD (PD +, PD-) which has a some light-receiving surface, an outward path, and a return path | route FIG. 8B is a diagram showing a relationship between detection signals of PD (PD +, PD−) in FIG. 5B and FIG. 8B is a diagram showing an arrangement example of two light receiving surfaces (PD) of the synchronization detection PD. It is a figure which shows the change of the image height by the detection signal by the synchronous detection PD (PD +, PD-) of this invention of FIG. 5, and the deflection scanning of a vibration mirror. It is a figure which shows the time chart about the graph of a vibration mirror at the time of installing synchronous detection PD + and synchronous detection PD- in the both outer sides of an image formation area (vertical axis deflection angle, horizontal axis time), and LD lighting timing. It is a schematic diagram when the vibration state of a vibration mirror changes. + The time t1 from when the light beam scanned by the vibrating mirror passes through the synchronization detection PD installed on the image height side to reach the maximum amplitude and return again, and the light beam scanned by the synchronization detection PD are similarly synchronized. It is a figure which shows an example of the relationship with time t2 until it passes detection PD. + The time t1 from when the light beam scanned by the vibrating mirror passes through the synchronization detection PD installed on the image height side to reach the maximum amplitude and return again, and the light beam scanned by the synchronization detection PD are similarly synchronized. It is a figure which shows another example of the relationship with time t2 until it passes detection PD. + The time t1 from when the light beam scanned by the vibrating mirror passes through the synchronization detection PD installed on the image height side to reach the maximum amplitude and return again, and the light beam scanned by the synchronization detection PD are similarly synchronized. It is a figure which shows another example of the relationship with time t2 until it passes detection PD. It is a figure which shows the structural example of the vibration mirror used for the deflection | deviation means of the optical scanning device of this invention. It is a block diagram which shows the structural example of the light source drive circuit (light source drive means) which drives a light source (LD), and the vibration mirror drive circuit (deflection control means) which amplitudes a vibration mirror. It is a figure which shows the relationship between the frequency f which switches the direction through which the electric current sent through the plane coil of a vibration mirror flows, and deflection angle (theta). It is a figure which shows the time change of the scanning angle (deflection angle) of a vibration mirror, and the detection signal in a synchronous detection sensor. It is a figure which shows the time change of the scanning angle (deflection angle) of a vibration mirror. It is a block diagram which shows the detail of the drive circuit for modulating the semiconductor laser which is a light emission source. It is a figure which shows the example which shifted the phase of arbitrary pixels. 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. It is a figure which shows typically the mode of the reflected light when the reflective surface of a vibration mirror deform | transforms. It is a disassembled perspective view which shows the structural example of the optical housing of an optical scanning device. It is a schematic block diagram which shows the structural example of the image forming apparatus carrying the optical scanning device shown in FIG.

Explanation of symbols

101, 102, 103, 104, 901: Photosensitive drum (scanned surface)
106: Vibration mirror (deflection means)
107, 108, 252: Light source unit 113: Cylindrical lens 120, 254: Scan lens 122-125: Toroidal lens 126-132: Folding mirror 138: Synchronization detection sensor (synchronization detection PD)
139: Imaging lens for synchronization detection 201-204: Light beam 250: Optical housing 253: Vibration mirror module 301: Light source driving means 302: Light beam detection means 303: Pixel clock / count measurement means 304: Deflection control means 440: Vibration Mirror substrate 441: Vibration mirror surface (movable mirror)
442: Torsion beam 443: Diaphragm 444: Reinforcement beam 446: Frame 447: Support member (frame)
448: Mounting board 449: Circuit board 450: Permanent magnet 454: Connector 460: Vibration mirror 463: Coil pattern 464: Terminal 470: Yoke 601: Drive control part of vibration mirror 602: Gain adjustment part 603: Movable mirror drive part 604: Light source drive unit 605: Write control unit 606: Pixel clock generation unit 607: Amplitude calculation unit 900: Optical scanning device 902: Charge charger 903: Development roller 904: Development device 905: Cleaning device 906: Intermediate transfer belt 907: Paper feed Tray 908: paper feed roller 909: registration roller pair 910: secondary transfer device 911: fixing device 912: paper discharge roller pair 913: paper discharge tray

Claims (10)

Light source means for emitting a light beam;
Light source driving means for modulating and driving the light source means;
Deflection means for reciprocatingly scanning the main scanning region by deflecting the light beam emitted from the light source means;
A scanning imaging optical system for guiding the light beam from the deflecting means onto the surface to be scanned;
A light beam detecting means for detecting a light beam from the deflecting means,
One or more of the light beam detecting means are arranged in the main scanning direction, and the light beam detecting means has a plurality of light receiving surfaces for detecting the light beam and has a light receiving surface adjacent to the main scanning direction. In an optical scanning device,
The width of the boundary between the light receiving surfaces adjacent in the main scanning direction is Δw [μm], the time during which the light beam passes through the boundary of the light receiving surface is dt [ns], the scanning frequency of the deflecting means is fd [Hz], and the image When the effective scanning period ratio of the region is μ and the main scanning writing width is W [mm],
Δw <W × dt / {μ / (2 × fd)} × 1000
An optical scanning device characterized by being set so as to satisfy the relational expression: The optical scanning device according to claim 1,
When the width in the main scanning direction of the boundary between the adjacent light receiving surfaces is Δw [μm] and the main scanning beam diameter of the light beam on the surface to be scanned is φm [μm],
Δw <φm × 0.125
An optical scanning device characterized in that the light receiving surface is arranged so as to satisfy the relational expression: The optical scanning device according to claim 1 or 2,
The light source means has a plurality of light emitting portions for emitting a light beam,
The light source driving means modulates and drives a plurality of light emitting units of the light source means,
When the light beam detecting means detects a light beam that is reciprocally scanned by the deflecting means and passes through the light receiving surface, the light source driving means controls a light emission amount of a plurality of light emitting portions of the light source means, An optical scanning device that detects and detects a light beam to be detected from the light beams. In the optical scanning device according to any one of claims 1 to 3,
The light source means has a plurality of light emitting units for emitting a light beam,
The light source driving means modulates and drives a plurality of light emitting units of the light source means,
The deflection means deflects the light beam emitted from the light source means to reciprocate the main scanning area,
The scanning imaging optical system guides the light beam from the deflecting means onto the surface to be scanned,
The light beam detection means is configured to detect a light beam from the deflection means with one or more light receiving surfaces,
When the maximum deflection angle of the reflecting surface of the deflecting unit is larger than the incident angle of the light beam emitted from the light source unit to the reflecting surface of the deflecting unit,
The light source driving means controls the timing and width of the light emission amount control period of the light emitting part forcibly turning off the light source means based on the detection signal detected by the light beam detecting means. apparatus. In the optical scanning device according to any one of claims 1 to 4,
The optical scanning device characterized in that the deflecting means is a vibrating mirror supported by a torsion beam and deflects a light beam from the light source means to reciprocately scan a main scanning region. In the optical scanning device according to any one of claims 1 to 5,
The deflection control means controls the timing and time setting of the light emission amount control period by the light source driving means according to the shift amount of the amplitude center of the deflection means calculated based on the detection signal detected by the light beam detection means. An optical scanning device. In the optical scanning device according to any one of claims 1 to 5,
An optical scanning apparatus characterized in that the deflection control means controls the maximum amplitude of the deflection means to be constant based on a detection signal detected by the light beam detection means. In the optical scanning device according to any one of claims 1 to 5,
The deflection control means controls the timing and time setting of the light emission amount control period by the light source driving means according to the scanning frequency of the deflection means calculated based on the detection signal detected by the light beam detection means. An optical scanning device. In the optical scanning device according to any one of claims 6 to 8,
The optical scanning device characterized in that the deflection means is controlled by the deflection control means. An image forming apparatus comprising: at least one image carrier; and at least one optical scanning device that scans the at least one image carrier with a light beam including image information.
An image forming apparatus comprising the optical scanning device according to claim 1 as the optical scanning device.

Images